Method and apparatus for processing video signals on basis of inter prediction

ABSTRACT

A method for processing video signals on the basis of inter prediction includes the steps of: deriving a motion vector predictor by using motion information of a neighboring block of the current block; parsing layer information for indicating the current layer, to which a motion vector difference used for the inter prediction of the current block belongs, within a predefined layer structure in which a combination of motion vector differences between one or more horizontal and vertical components is classified into a plurality of layers; parsing index information for indicating a specific combination in the current layer; deriving a motion vector difference of the current block by using the layer information and the index information; and deriving a motion vector of the current block by adding the motion vector difference to the motion vector predictor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2019/012354, filed on Sep. 23, 2019,which claims the benefit of U.S. Provisional Applications No.62/735,028, filed on Sep. 22, 2018, the contents of which are all herebyincorporated by reference herein in their entirety.

TECHNICAL FIELD

Embodiments of the disclosure relate to methods and devices forprocessing video signals based on inter prediction, and specifically, tomethods for vector-coding a motion vector difference used for interprediction and devices therefor.

BACKGROUND ART

Compression encoding means a series of signal processing techniques fortransmitting digitized information through a communication line ortechniques for storing information in a form suitable for a storagemedium. The medium including a picture, an image, audio, etc. may be atarget for compression encoding, and particularly, a technique forperforming compression encoding on a picture is referred to as videoimage compression.

Next-generation video contents are supposed to have the characteristicsof high spatial resolution, a high frame rate and high dimensionality ofscene representation. In order to process such contents, a drasticincrease in the memory storage, memory access rate and processing powerwill result.

Accordingly, it is required to design a coding tool for processingnext-generation video contents efficiently.

DETAILED DESCRIPTION OF THE DISCLOSURE Technical Problem

Embodiments of the disclosure aim to propose vector coding techniquesfor jointly coding horizontal and vertical components of a motion vectordifference using the correlation between motion vector differences.

Objects of the disclosure are not limited to the foregoing, and otherunmentioned objects would be apparent to one of ordinary skill in theart from the following description.

Technical Solution

According to an embodiment of the disclosure, a method for processing avideo signal based on inter prediction may comprise deriving a motionvector predictor using motion information for a neighboring block of acurrent block, parsing layer information indicating a current layer towhich a motion vector difference used for inter prediction of thecurrent block belongs, in a predefined layer structure in whichcombinations of at least one horizontal and vertical components ofmotion vector differences are divided into a plurality of layers,parsing index information indicating a specific combination in thecurrent layer, deriving a motion vector difference of the current blockusing the layer information and the index information, and deriving amotion vector of the current block by adding the motion vectordifference to the motion vector predictor.

Preferably, parsing the layer information may include parsing a firstflag indicating whether an identification (ID) of the current layer islarger than 0 and, when the ID of the current layer is 0, parsing asecond flag indicating whether the ID of the current layer is largerthan 1.

Preferably, parsing the layer information may include parsing remaininglayer information indicating the current layer among layers whose IDsare equal to or larger than 2 when the ID of the current layer is largerthan 1.

Preferably, the remaining layer information may be binarized using anexponential Golomb code having an order of 1.

Preferably, the index information may be binarized using a truncatedbinarization method.

Preferably, the method may further comprise generating a predictionsample of the current block by performing inter prediction using themotion vector of the current block.

According to another embodiment of the disclosure, a device for decodinga video signal based on inter prediction may comprise a memory storingthe video signal and a processor coupled with the memory, wherein theprocessor may derive a motion vector predictor using motion informationfor a neighboring block of a current block, parse layer informationindicating a current layer to which a motion vector difference used forinter prediction of the current block belongs, in a predefined layerstructure in which combinations of at least one horizontal and verticalcomponents of motion vector differences are divided into a plurality oflayers, parse index information indicating a specific combination in thecurrent layer, derive a motion vector difference of the current blockusing the layer information and the index information, and derive amotion vector of the current block by adding the motion vectordifference to the motion vector predictor.

Advantageous Effects

According to conventional video compression techniques, the horizontalcomponent and the vertical component of the MVD are individuallyencoded/decoded. However, as described above, according to data analysisbased on frequency analysis, the horizontal component and the verticalcomponent of the MVD may have a mutual correlation and are highly likelyto belong to the same layer in the layer structure according to anembodiment of the disclosure.

Accordingly, according to an embodiment of the disclosure, the MVDcoding efficiency may be significantly increased by coding thehorizontal and vertical components of the MVD together based on layerinformation and index information.

Effects of the disclosure are not limited to the foregoing, and otherunmentioned effects would be apparent to one of ordinary skill in theart from the following description.

BRIEF DESCRIPTION OF DRAWINGS

In order to help understanding of the disclosure, the accompanyingdrawings which are included as a part of the Detailed Descriptionprovide embodiments of the disclosure and describe the technicalfeatures of the disclosure together with the Detailed Description.

FIG. 1 is a schematic block diagram of an encoding apparatus in whichencoding of a video/image signal is performed as an embodiment to whichthe disclosure is applied.

FIG. 2 is a schematic block diagram of a decoding apparatus in whichdecoding of a video/image signal is performed as an embodiment to whichthe disclosure is applied.

FIG. 3 is a diagram illustrating an example of a multi-type treestructure to which the disclosure may be applied.

FIG. 4 is a diagram illustrating a signaling mechanism of partitioninginformation of a quadtree having a nested multi-type tree structure asan embodiment to which the disclosure may be applied.

FIG. 5 is a diagram illustrating a method for splitting a CTU intomultiple CUs based on a quadtree and nested multi-type tree structure asan embodiment to which the disclosure may be applied.

FIG. 6 is a diagram illustrating a method for limiting ternary-treesplitting as an embodiment to which the disclosure may be applied.

FIG. 7 is a diagram illustrating redundant partitioning patterns whichmay occur in binary-tree partitioning and ternary-tree partitioning asan embodiment to which the disclosure may be applied.

FIGS. 8 and 9 are diagrams illustrating an inter prediction basedvideo/image encoding method according to an embodiment of the disclosureand an inter prediction unit in an encoding apparatus according to anembodiment of the disclosure.

FIGS. 10 and 11 are diagrams illustrating an inter prediction basedvideo/image decoding method according to an embodiment of the disclosureand an inter prediction unit in a decoding apparatus according to anembodiment of the disclosure.

FIG. 12 is a diagram for describing a neighboring block used in a mergemode or a skip mode as an embodiment to which the disclosure is applied.

FIG. 13 is a flowchart illustrating a method for configuring a mergingcandidate list according to an embodiment to which the disclosure isapplied.

FIG. 14 is a flowchart illustrating a method for configuring a mergingcandidate list according to an embodiment to which the disclosure isapplied.

FIG. 15 illustrates an example of motion models according to anembodiment of the disclosure.

FIG. 16 illustrates an example of a control point motion vector for anaffine motion prediction according to an embodiment of the disclosure.

FIG. 17 illustrates an example of a motion vector for each subblock of ablock to which an affine motion prediction according to an embodiment ofthe disclosure has been applied.

FIG. 18 illustrates an example of neighboring blocks used for an affinemotion prediction in an affine merge mode according to an embodiment ofthe disclosure.

FIG. 19 illustrates an example in which a block on which an affinemotion prediction is performed using neighboring blocks to which anaffine motion prediction according to an embodiment of the disclosurehas been applied.

FIG. 20 is a diagram for describing a method of generating a mergecandidate list using peripheral affine coding blocks according to anembodiment of the disclosure.

FIGS. 21 and 22 are diagrams for describing a method of configuring anaffine merge candidate list using a neighboring block encoded by anaffine prediction according to an embodiment of the disclosure.

FIG. 23 illustrates an example of neighboring blocks used for an affinemotion prediction in an affine inter mode according to an embodiment ofthe disclosure.

FIG. 24 illustrates an example of neighboring blocks used for an affinemotion prediction in the affine inter mode according to an embodiment ofthe disclosure.

FIGS. 25 and 26 are diagrams illustrating a method of deriving motionvector candidates using motion information of neighboring blocks in theaffine inter mode according to an embodiment of the disclosure.

FIG. 27 illustrates an example of a method of deriving an affine motionvector field in a subblock unit according to an embodiment of thedisclosure.

FIG. 28 illustrates a method of generating a prediction block and amotion vector in an inter prediction to which an affine motion modelaccording to an embodiment of the disclosure has been applied.

FIG. 29 is a diagram illustrating a method of performing a motioncompensation based on a motion vector of a control point according to anembodiment of the disclosure.

FIG. 30 is a diagram illustrating a method of performing a motioncompensation based on motion vectors of control points in a nonregularblock according to an embodiment of the disclosure.

FIG. 31 is a diagram illustrating a method of performing a motioncompensation based on motion vectors of control points in a nonregularblock according to an embodiment of the disclosure.

FIGS. 32 to 38 are diagrams illustrating a method of performing a motioncompensation based on motion vectors of control points in a nonregularblock according to an embodiment of the disclosure.

FIG. 39 illustrates an overall coding structure for deriving a motionvector according to an embodiment of the disclosure.

FIG. 40 illustrates an example of an MVD coding structure according toan embodiment of the disclosure.

FIG. 41 illustrates an example of an MVD coding structure according toan embodiment of the disclosure.

FIG. 42 illustrates an example of an MVD coding structure according toan embodiment of the disclosure.

FIG. 43 illustrates an example of an MVD coding structure according toan embodiment of the disclosure.

FIG. 44 is a view illustrating a method for deriving affine motionvector difference information according to an embodiment of thedisclosure.

FIG. 45 is a view illustrating a method for deriving motion vectordifference information based on a threshold according to an embodimentof the disclosure.

FIG. 46 is a view illustrating a vector coding method for an affinemotion vector difference according to an embodiment of the disclosure.

FIG. 47 is a view illustrating a vector coding method for an affinemotion vector difference according to an embodiment of the disclosure.

FIG. 48 is a parsing flowchart for MVD components according to anembodiment of the disclosure.

FIG. 49 is a view illustrating a coding structure of a motion vectordifference performed based on vector coding according to an embodimentof the disclosure.

FIG. 50 is a view illustrating a coding structure of a motion vectordifference performed based on vector coding according to an embodimentof the disclosure.

FIG. 51 is a view illustrating a vector coding method for a motionvector difference according to an embodiment of the disclosure.

FIG. 52 is a view illustrating a vector coding method for a motionvector difference based on a layer structure according to an embodimentof the disclosure.

FIG. 53 is a view illustrating an example structure of a decodingapparatus according to an embodiment of the disclosure.

FIG. 54 is a view illustrating an example structure of an encodingapparatus according to an embodiment.

FIG. 55 is a flowchart illustrating a method for processing a videosignal based on inter prediction according to an embodiment of thedisclosure.

FIG. 56 is a block diagram illustrating an example device for processingvideo signals according to an embodiment of the disclosure.

FIG. 57 illustrates a video coding system according to the disclosure.

FIG. 58 is a view illustrating a structure of a content streaming systemaccording to an embodiment of the disclosure.

MODE FOR CARRYING OUT THE DISCLOSURE

Hereinafter, preferred embodiments of the disclosure are described indetail with reference to the accompanying drawings. A detaileddescription to be disclosed along with the accompanying drawings areintended to describe some embodiments of the disclosure and are notintended to describe a sole embodiment of the disclosure. The followingdetailed description includes more details in order to provide fullunderstanding of the disclosure. However, those skilled in the art willunderstand that the disclosure may be implemented without such moredetails.

In some cases, in order to avoid that the concept of the disclosurebecomes vague, known structures and devices are omitted or may be shownin a block diagram form based on the core functions of each structureand device.

Although most terms used in the disclosure have been selected fromgeneral ones widely used in the art, some terms have been arbitrarilyselected by the applicant and their meanings are explained in detail inthe following description as needed. Thus, the disclosure should beunderstood with the intended meanings of the terms rather than theirsimple names or meanings.

Specific terms used in the following description have been provided tohelp understanding of the disclosure, and the use of such specific termsmay be changed in various forms without departing from the technicalsprit of the disclosure. For example, signals, data, samples, pictures,frames, blocks and the like may be appropriately replaced andinterpreted in each coding process.

In the present description, a “processing unit” refers to a unit inwhich an encoding/decoding process such as prediction, transform and/orquantization is performed. Hereinafter, for convenience of description,the processing unit may be referred to as a ‘processing block’ or a‘block’.

Further, the processing unit may be interpreted into the meaningincluding a unit for a luma component and a unit for a chroma component.For example, the processing unit may correspond to a coding tree unit(CTU), a coding unit (CU), a prediction unit (PU) or a transform unit(TU).

In addition, the processing unit may be interpreted into a unit for aluma component or a unit for a chroma component. For example, theprocessing unit may correspond to a coding tree block (CTB), a codingblock (CB), a prediction unit PU or a transform block (TB) for the lumacomponent. Further, the processing unit may correspond to a CTB, a CB, aPU or a TB for the chroma component. Moreover, the processing unit isnot limited thereto and may be interpreted into the meaning including aunit for the luma component and a unit for the chroma component.

In addition, the processing unit is not necessarily limited to a squareblock and may be configured as a polygonal shape having three or morevertexes.

Furthermore, in the present description, a pixel is called a sample. Inaddition, using a sample may mean using a pixel value or the like.

FIG. 1 is a schematic block diagram of an encoding apparatus whichencodes a video/image signal as an embodiment to which the disclosure isapplied.

Referring to FIG. 1, an encoding apparatus 100 may be configured toinclude an image divider 110, a subtractor 115, a transformer 120, aquantizer 130, a dequantizer 140, an inverse transformer 150, an adder155, a filter 160, a memory 170, an inter predictor 180, an intrapredictor 185 and an entropy encoder 190. The inter predictor 180 andthe intra predictor 185 may be commonly called a predictor. In otherwords, the predictor may include the inter predictor 180 and the intrapredictor 185. The transformer 120, the quantizer 130, the dequantizer140, and the inverse transformer 150 may be included in a residualprocessor. The residual processor may further include the subtractor115. In one embodiment, the image divider 110, the subtractor 115, thetransformer 120, the quantizer 130, the dequantizer 140, the inversetransformer 150, the adder 155, the filter 160, the inter predictor 180,the intra predictor 185 and the entropy encoder 190 may be configured asone hardware component (e.g., an encoder or a processor). Furthermore,the memory 170 may include a decoded picture buffer (DPB), and may beimplemented by a digital storage medium.

The image divider 110 may divide an input image (or picture or frame),input to the encoding apparatus 100, into one or more processing units.For example, the processing unit may be called a coding unit (CU). Inthis case, the coding unit may be recursively split from a coding treeunit (CTU) or the largest coding unit (LCU) based on a quadtreebinary-tree (QTBT) structure. For example, one coding unit may be splitinto a plurality of coding units of a deeper depth based on a quadtreestructure and/or a binary-tree structure. In this case, for example, thequadtree structure may be first applied, and the binary-tree structuremay be then applied. Alternatively the binary-tree structure may befirst applied. A coding procedure according to the disclosure may beperformed based on the final coding unit that is no longer split. Inthis case, the largest coding unit may be directly used as the finalcoding unit based on coding efficiency according to an imagecharacteristic or a coding unit may be recursively split into codingunits of a deeper depth, if necessary. Accordingly, a coding unit havingan optimal size may be used as the final coding unit. In this case, thecoding procedure may include a procedure, such as a prediction,transform or reconstruction to be described later. For another example,the processing unit may further include a prediction unit (PU) or atransform unit (TU). In this case, each of the prediction unit and thetransform unit may be divided or partitioned from each final codingunit. The prediction unit may be a unit for sample prediction, and thetransform unit may be a unit from which a transform coefficient isderived and/or a unit in which a residual signal is derived from atransform coefficient.

A unit may be interchangeably used with a block or an area according tocircumstances. In a common case, an M×N block may indicate a set ofsamples configured with M columns and N rows or a set of transformcoefficients. In general, a sample may indicate a pixel or a value of apixel, and may indicate only a pixel/pixel value of a luma component oronly a pixel/pixel value of a chroma component. In a sample, one picture(or image) may be used as a term corresponding to a pixel or pel.

The encoding apparatus 100 may generate a residual signal (residualblock or residual sample array) by subtracting a prediction signal(predicted block or prediction sample array), output by the interpredictor 180 or the intra predictor 185, from an input image signal(original block or original sample array). The generated residual signalis transmitted to the transformer 120. In this case, as illustrated, aunit in which the prediction signal (prediction block or predictionsample array) is subtracted from the input image signal (original blockor original sample array) within the encoding apparatus 100 may becalled the subtractor 115. The predictor may perform prediction on aprocessing target block (hereinafter referred to as a current block),and may generate a predicted block including prediction samples for thecurrent block. The predictor may determine whether an intra predictionis applied or inter prediction is applied in a current block or a CUunit. The predictor may generate various pieces of information on aprediction, such as prediction mode information as will be describedlater in the description of each prediction mode, and may transmit theinformation to the entropy encoder 190. The information on predictionmay be encoded in the entropy encoder 190 and may be output in abitstream form.

The intra predictor 185 may predict a current block with reference tosamples within a current picture. The referred samples may be located toneighbor the current block or may be spaced from the current blockdepending on a prediction mode. In an intra prediction, prediction modesmay include a plurality of non-angular modes and a plurality of angularmodes. The non-angular mode may include a DC mode and a planar mode, forexample. The angular mode may include 33 angular prediction modes or 65angular prediction modes, for example, depending on a fine degree of aprediction direction. In this case, angular prediction modes that aremore or less than the 33 angular prediction modes or 65 angularprediction modes may be used depending on a configuration, for example.The intra predictor 185 may determine a prediction mode applied to acurrent block using the prediction mode applied to a neighboring block.

The inter predictor 180 may derive a predicted block for a current blockbased on a reference block (reference sample array) specified by amotion vector on a reference picture. In this case, in order to reducethe amount of motion information transmitted in an inter predictionmode, motion information may be predicted as a block, a sub-block or asample unit based on the correlation of motion information between aneighboring block and the current block. The motion information mayinclude a motion vector and a reference picture index. The motioninformation may further include inter prediction direction (L0prediction, L1 prediction, Bi prediction) information. In the case ofinter prediction, a neighboring block may include a spatial neighboringblock within a current picture and a temporal neighboring block within areference picture. A reference picture including a reference block and areference picture including a temporal neighboring block may be the sameor different. The temporal neighboring block may be referred to as aname called a co-located reference block or a co-located CU (colCU). Areference picture including a temporal neighboring block may be referredto as a co-located picture (colPic). For example, the inter predictor180 may construct a motion information candidate list based onneighboring blocks, and may generate information indicating that whichcandidate is used to derive a motion vector and/or reference pictureindex of a current block. An inter prediction may be performed based onvarious prediction modes. For example, in the case of a skip mode and amerge mode, the inter predictor 180 may use motion information of aneighboring block as motion information of a current block. In the caseof the skip mode, unlike the merge mode, a residual signal may not betransmitted. In the case of a motion vector prediction (MVP) mode, amotion vector of a neighboring block may be used as a motion vectorpredictor. A motion vector of a current block may be indicated bysignaling a motion vector difference.

A prediction signal generated through the inter predictor 180 or theintra predictor 185 may be used to generate a reconstructed signal or aresidual signal.

The transformer 120 may generate transform coefficients by applying atransform scheme to a residual signal. For example, the transform schememay include at least one of a discrete cosine transform (DCT), adiscrete sine transform (DST), a Karhunen-Loève transform (KLT), agraph-based transform (GBT), or a conditionally non-linear transform(CNT). In this case, the GBT means a transform obtained from a graph ifrelation information between pixels is represented as the graph. The CNTmeans a transform obtained based on a prediction signal generated u singall of previously reconstructed pixels. Furthermore, a transform processmay be applied to pixel blocks having the same size of a square form ormay be applied to blocks having variable sizes not a square form.

The quantizer 130 may quantize transform coefficients and transmit themto the entropy encoder 190. The entropy encoder 190 may encode aquantized signal (information on quantized transform coefficients) andoutput it in a bitstream form. The information on quantized transformcoefficients may be called residual information. The quantizer 130 mayre-arrange the quantized transform coefficients of a block form inone-dimensional vector form based on a coefficient scan sequence, andmay generate information on the quantized transform coefficients basedon the quantized transform coefficients of the one-dimensional vectorform. The entropy encoder 190 may perform various encoding methods, suchas exponential Golomb, context-adaptive variable length coding (CAVLC),and context-adaptive binary arithmetic coding (CABAC). The entropyencoder 190 may encode information (e.g., values of syntax elements)necessary for video/image reconstruction in addition to the quantizedtransform coefficients together or separately. The encoded information(e.g., encoded video/image information) may be transmitted or stored ina network abstraction layer (NAL) unit in the form of a bitstream. Thebitstream may be transmitted over a network or may be stored in adigital storage medium. In this case, the network may include abroadcast network and/or a communication network. The digital storagemedium may include various storage media, such as a USB, an SD, a CD, aDVD, Blu-ray, an HDD, and an SSD. A transmitter (not illustrated) thattransmits a signal output by the entropy encoder 190 and/or a storage(not illustrated) for storing the signal may be configured as aninternal/external element of the encoding apparatus 100, or thetransmitter may be an element of the entropy encoder 190.

Quantized transform coefficients output by the quantizer 130 may be usedto generate a prediction signal. For example, a residual signal may bereconstructed by applying de-quantization and an inverse transform tothe quantized transform coefficients through the dequantizer 140 and theinverse transformer 150 within a loop. The adder 155 may add thereconstructed residual signal to a prediction signal output by the interpredictor 180 or the intra predictor 185, so a reconstructed signal(reconstructed picture, reconstructed block or reconstructed samplearray) may be generated. A predicted block may be used as areconstructed block if there is no residual for a processing targetblock as in the case where a skip mode has been applied. The adder 155may be called a reconstructor or a reconstruction block generator. Thegenerated reconstructed signal may be used for the intra prediction of anext processing target block within a current picture, and may be usedfor the inter prediction of a next picture through filtering as will bedescribed later.

The filter 160 can improve subjective/objective picture quality byapplying filtering to a reconstructed signal. For example, the filter160 may generate a modified reconstructed picture by applying variousfiltering methods to the reconstructed picture. The modifiedreconstructed picture may be stored in the memory 170, more particularlyin the DPB of the memory 170. The various filtering methods may includedeblocking filtering, a sample adaptive offset, an adaptive loop filter,and a bilateral filter, for example. The filter 160 may generate variouspieces of information for filtering as will be described later in thedescription of each filtering method, and may transmit them to theentropy encoder 190. The filtering information may be encoded by theentropy encoder 190 and output in a bitstream form.

The modified reconstructed picture transmitted to the memory 170 may beused as a reference picture in the inter predictor 180. The encodingapparatus can avoid a prediction mismatch in the encoding apparatus 100and a decoding apparatus and improve encoding efficiency if interprediction is applied.

The DPB of the memory 170 may store the modified reconstructed pictureto use it as a reference picture in the inter predictor 180. The memory170 may store motion information of a block in which the motioninformation in the current picture is derived (or encoded) and/or motioninformation of blocks in an already reconstructed picture. The storedmotion information may be forwarded to the inter predictor 180 to beutilized as motion information of a spatial neighboring block or motioninformation of a temporal neighboring block. The memory 170 may storereconstructed samples of the reconstructed blocks in the current pictureand forward it to the intra predictor 185.

FIG. 2 is an embodiment to which the disclosure is applied, and is aschematic block diagram of a decoding apparatus for decoding avideo/image signal.

Referring to FIG. 2, the decoding apparatus 200 may be configured toinclude an entropy decoder 210, a dequantizer 220, an inversetransformer 230, an adder 235, a filter 240, a memory 250, an interpredictor 260 and an intra predictor 265. The inter predictor 260 andthe intra predictor 265 may be collectively called a predictor. That is,the predictor may include the inter predictor 180 and the intrapredictor 185. The dequantizer 220 and the inverse transformer 230 maybe collectively called as residual processor. That is, the residualprocessor may include the dequantizer 220 and the inverse transformer230. The entropy decoder 210, the dequantizer 220, the inversetransformer 230, the adder 235, the filter 240, the inter predictor 260and the intra predictor 265 may be configured as one hardware component(e.g., the decoder or the processor) according to an embodiment.Furthermore, the memory 250 may include a decoded picture buffer (DPB),and may be implemented by a digital storage medium.

When a bitstream including video/image information is input, thedecoding apparatus 200 may reconstruct an image in accordance with aprocess of processing video/image information in the encoding apparatusof FIG. 1. For example, the decoding apparatus 200 may perform decodingusing a processing unit applied in the encoding apparatus. Accordingly,a processing unit for decoding may be a coding unit, for example. Thecoding unit may be split from a coding tree unit or the largest codingunit depending on a quadtree structure and/or a binary-tree structure.Furthermore, a reconstructed image signal decoded and output through thedecoding apparatus 200 may be played back through a playback device.

The decoding apparatus 200 may receive a signal, output by the encodingapparatus of FIG. 1, in a bitstream form. The received signal may bedecoded through the entropy decoder 210. For example, the entropydecoder 210 may derive information (e.g., video/image information) forimage reconstruction (or picture reconstruction) by parsing thebitstream. For example, the entropy decoder 210 may decode informationwithin the bitstream based on a coding method, such as exponentialGolomb encoding, CAVLC or CABAC, and may output a value of a syntaxelement for image reconstruction or quantized values of transformcoefficients regarding a residual. More specifically, in the CABACentropy decoding method, a bin corresponding to each syntax element maybe received from a bitstream, a context model may be determined usingdecoding target syntax element information and decoding information of aneighboring and decoding target block or information of a symbol/bindecoded in a previous step, a probability that a bin occurs may bepredicted based on the determined context model, and a symbolcorresponding to a value of each syntax element may be generated byperforming arithmetic decoding on the bin. In this case, in the CABACentropy decoding method, after a context model is determined, thecontext model may be updated using information of a symbol/bin decodedfor the context model of a next symbol/bin. Information on a predictionamong information decoded in the entropy decoder 2110 may be provided tothe predictor (inter predictor 260 and intra predictor 265). Parameterinformation related to a residual value on which entropy decoding hasbeen performed in the entropy decoder 210, that is, quantized transformcoefficients, may be input to the dequantizer 220. Furthermore,information on filtering among information decoded in the entropydecoder 210 may be provided to the filter 240. Meanwhile, a receiver(not illustrated) that receives a signal output by the encodingapparatus may be further configured as an internal/external element ofthe decoding apparatus 200 or the receiver may be an element of theentropy decoder 210.

The dequantizer 220 may de-quantize quantized transform coefficients andoutput transform coefficients. The dequantizer 220 may re-arrange thequantized transform coefficients in a two-dimensional block form. Inthis case, the re-arrangement may be performed based on a coefficientscan sequence performed in the encoding apparatus. The dequantizer 220may perform de-quantization on the quantized transform coefficientsusing a quantization parameter (e.g., quantization step sizeinformation), and may obtain transform coefficients.

The inverse transformer 230 may output a residual signal (residual blockor residual sample array) by applying inverse-transform to transformcoefficients.

The predictor may perform a prediction on a current block, and maygenerate a predicted block including prediction samples for the currentblock. The predictor may determine whether an intra prediction isapplied or inter prediction is applied to the current block based oninformation on a prediction, which is output by the entropy decoder 210,and may determine a detailed intra/inter prediction mode.

The intra predictor 265 may predict a current block with reference tosamples within a current picture. The referred samples may be located toneighbor a current block or may be spaced apart from a current blockdepending on a prediction mode. In an intra prediction, prediction modesmay include a plurality of non-angular modes and a plurality of angularmodes. The intra predictor 265 may determine a prediction mode appliedto a current block using a prediction mode applied to a neighboringblock.

The inter predictor 260 may derive a predicted block for a current blockbased on a reference block (reference sample array) specified by amotion vector on a reference picture. In this case, in order to reducethe amount of motion information transmitted in an inter predictionmode, motion information may be predicted as a block, a sub-block or asample unit based on the correlation of motion information between aneighboring block and the current block. The motion information mayinclude a motion vector and a reference picture index. The motioninformation may further include inter prediction direction (L0prediction, L1 prediction, Bi prediction) information. In the case ofinter prediction, a neighboring block may include a spatial neighboringblock within a current picture and a temporal neighboring block within areference picture. For example, the inter predictor 260 may configure amotion information candidate list based on neighboring blocks, and mayderive a motion vector and/or reference picture index of a current blockbased on received candidate selection information. An inter predictionmay be performed based on various prediction modes. Information on theprediction may include information indicating a mode of inter predictionfor a current block.

The adder 235 may generate a reconstructed signal (reconstructedpicture, reconstructed block or reconstructed sample array) by adding anobtained residual signal to a prediction signal (predicted block orprediction sample array) output by the inter predictor 260 or the intrapredictor 265. A predicted block may be used as a reconstructed block ifthere is no residual for a processing target block as in the case wherea skip mode has been applied.

The adder 235 may be called a reconstructor or a reconstruction blockgenerator. The generated reconstructed signal may be used for the intraprediction of a next processing target block within a current picture,and may be used for the inter prediction of a next picture throughfiltering as will be described later.

The filter 240 can improve subjective/objective picture quality byapplying filtering to a reconstructed signal. For example, the filter240 may generate a modified reconstructed picture by applying variousfiltering methods to a reconstructed picture, and may transmit themodified reconstructed picture to the memory 250, more particularly tothe DPB of the memory 250. The various filtering methods may includedeblocking filtering, a sample adaptive offset SAO, an adaptive loopfilter ALF, and a bilateral filter, for example.

The (modified) reconstructed picture stored in the DPB of the memory 250may be used as a reference picture in the inter predictor 260. Thememory 250 may store motion information of a block in which the motioninformation in the current picture is derived (or decoded) and/or motioninformation of blocks in an already reconstructed picture. The storedmotion information may be forwarded to the inter predictor 260 to beutilized as motion information of a spatial neighboring block or motioninformation of a temporal neighboring block. The memory 170 may storereconstructed samples of the reconstructed blocks in the current pictureand forward it to the intra predictor 265.

In the disclosure, the embodiments described in the filter 160, interpredictor 180 and intra predictor 185 of the encoding apparatus 100 maybe applied to the filter 240, inter predictor 260 and intra predictor265 of the decoding apparatus 200, respectively, identically or in acorrespondence manner.

Block Partitioning

The video/image coding method according to the disclosure may beperformed based on various detailed techniques, and each of the variousdetailed techniques is described as below. It is apparent to thoseskilled in the art that the techniques described herein may beassociated with the related procedure such as a prediction, a residualprocess ((inverse) transform, (de)quantization, etc.), a syntax elementcoding, a filtering, a partitioning/splitting in a video/imageencoding/decoding procedure described above and/or described below.

The block partitioning procedure according to the disclosure may beperformed in the image divider 110 of the encoding apparatus describedabove, and the partitioning related information may be (encoding)processed in the entropy encoder 190 and forwarded to the decodingapparatus in a bitstream format. The entropy decoder 210 of the decodingapparatus may obtain a block partitioning structure of a current picturebased on the partitioning related information obtained from thebitstream, and based on it, may perform a series of procedure (e.g.,prediction, residual processing, block reconstruction, in-loopfiltering, etc.) for an image decoding.

Partitioning of Picture into CTUs

Pictures may be divided into a sequence of coding tree units (CTUs). ACTU may correspond to a coding tree block (CTB). Alternatively, a CTUmay include a coding tree block of luma samples and two coding treeblocks of corresponding chroma samples. In other words, for a pictureincluding three types of sample arrays, a CTU may include an N×N blockof luma samples and two corresponding samples of chroma samples.

A maximum supported size of a CTU for coding and prediction may bedifferent from a maximum supported size of a CTU for transform. Forexample, a maximum supported size of luma block in a CTU may be 128×128.

Partitioning of the CTUs Using a Tree Structure

A CTU may be divided into CUs based on a quad-tree (QT) structure. Thequad-tree structure may be called as a quaternary structure. This is forreflecting various local characteristics. Meanwhile, in the disclosure,a CTU may be divided based on a multi-type tree structure partitioningincluding a binary-tree (BT) and a ternary-tree (TT) as well as thequad-tree. Hereinafter, QTBT structure may include the quad-tree andbinary-tree structures, and QTBTTT may include partitioning structuresbased on the binary-tree and ternary-tree. Alternatively, the QTBTstructure may also include partitioning structures based on thequad-tree, binary-tree and ternary-tree. In the coding tree structure, aCU may have a square or rectangle shape. A CTU may be divided into aquad-tree structure, first. And then, leaf nodes of the quad-treestructure may be additionally divided by the multi-type tree structure.

FIG. 3 is a diagram illustrating an example of a multi-type treestructure as an embodiment to which the disclosure may be applied.

In an embodiment of the disclosure, a multi-type tree structure mayinclude 4 split types as shown in FIG. 3. The 4 split types may includea vertical binary splitting (SPLIT_BT_VER), a horizontal binarysplitting (SPLIT_BT_HOR), a vertical ternary splitting (SPLIT_TT_VER)and a horizontal ternary splitting (SPLIT_TT_HOR). The leaf nodes of themulti-type tree structure may be called as CUs. Such CUs may be used forprediction and transform procedure. In the disclosure, generally, a CU,a PU and a TU may have the same block size. However, in the case that amaximum supported transform length is smaller than a width or a heightof a color component, a CU and a TU may have different block sizes.

FIG. 4 is a diagram illustrating a signaling mechanism of partitionsplit information of a quadtree having a nested multi-type treestructure as an embodiment to which the disclosure may be applied.

Here, a CTU may be treated as a root of a quad-tree and initiallypartitioned into a quad-tree structure. Each quad-tree leaf node may befurther partitioned into a multi-type tree structure later. In themulti-type tree structure, a first flag (e.g., mtt_split_cu_flag) issignaled to indicate whether the corresponding node is furtherpartitioned). In the case that the corresponding node is furtherpartitioned, a second flag (e.g., mtt_split_cu_verticla_flag) may besignaled to indicate a splitting direction. Later, a third flag (e.g.,mtt_split_cu_binary_flag) may be signaled to indicate whether the splittype is a binary split or a ternary split. For example, based on themtt_split_cu_vertical_flag and the mtt_split_cu_binary_flag, amulti-type tree splitting mode (MttSplitMode) may be derived asrepresented in Table 1 below.

TABLE 1 MttSplitMode mtt_split_cu_vertical_flag mtt_split_cu_binary_flagSPLIT_TT_HOR 0 0 SPLIT_BT_HOR 0 1 SPLIT_TT_VER 1 0 SPLIT_BT_VER 1 1

FIG. 5 is a diagram illustrating a method of partitioning a CTU intomultiple CUs based on a quadtree and nested multi-type tree structure asan embodiment to which the disclosure may be applied.

Here, bolded block edges represent a quad-tree partitioning, and theremaining edges represent a multi-type tree partitioning. The quad-treepartition with nested multi-type tree may provide a contents-adaptedcoding tree structure. A CU may correspond to a coding block (CB). Or, aCU may include a coding block of luma samples and two coding blocks ofcorresponding chroma samples. A size of CU may be great as much as a CTUor may be small as 4×4 in a luma sample unit. For example, in the caseof 4:2:0 color format (or chroma format), a maximum chroma CB size maybe 64×64, and a minimum chroma CB size may be 2×2.

In the disclosure, for example, a maximum supported luma TB size may be64×64, and a maximum supported chroma TB size may be 32×32. In the casethat a width or a height of a CB partitioned according to the treestructure is greater than a maximum transform width or height, the CBmay be further partitioned until a TB size limit in horizontal andvertical directions are satisfied automatically (or implicitly).

Meanwhile, for the quad-tree coding tree scheme with nested multi-typefree, the following parameters may be defined or recognized as SPSsyntax element.

-   -   CTU size: the root node size of a quaternary tree    -   MinQTSize: the minimum allowed quaternary tree leaf node size    -   MaxBtSize: the maximum allowed binary tree root node size    -   MaxTtSize: the maximum allowed ternary tree root node size    -   MaxMttDepth: the maximum allowed hierarchy depth of multi-type        tree splitting from a quadtree leaf    -   MinBtSize: the minimum allowed binary tree leaf node size    -   MinTtSize: the minimum allowed ternary tree leaf node size

As an example of the quad-tree coding tree scheme with nested multi-typetree, a CTU size may be set to 128×128 luma samples and 64×64 blocks oftwo corresponding chroma samples (in 4:2:0 chroma sample). In this case,MinOTSize may be set to 16×16, MaxBtSize may be set to 128×128,MaxTtSize may be set to 64×64, MinBtSize and MinTtSize (for both widthand height) may be set to 4×4, and MaxMttDepth may be set to 4. Thequad-tree partitioning may be applied to a CTU and generate quad-treeleaf nodes. The quad-tree leaf node may be called a leaf QT node. Thequad-tree leaf nodes may have a size from 16×16 size (i.e. theMinOTSize) to 128×128 size (i.e. the CTU size). In the case that a leafQT node is 128×128, the leaf QT node may not be partitioned into abinary-tree/ternary-tree. This is because the leaf QT node exceedsMaxBtsize and MaxTtsize (i.e., 64×64) even in the case the leaf QT nodeis partitioned. In other case, the leaf QT node may be additionallypartitioned into a multi-type tree. Therefore, the leaf QT node may be aroot node for the multi-type tree, and the leaf QT node may havemulti-type tree depth (mttDepth) 0 value. In the case that themulti-type tree depth reaches MaxMttdepth (e.g., 4), no more additionalpartition may be considered. In the case that a width of the multi-typetree node is equal to MinBtSize and smaller than or equal to2×MinTtSize, no more additional horizontal partitioning may beconsidered. In the case that a height of the multi-type tree node isequal to MinBtSize and smaller than or equal to 2×MinTtSize, no moreadditional vertical partitioning may be considered.

FIG. 6 is a diagram illustrating a method for limiting a ternary-treesplit as an embodiment to which the disclosure may be applied.

Referring to FIG. 6, in order to support 64×64 luma block and 32×32chroma pipeline design in a hardware decoder, a TT split may be limitedin a specific case. For example, in the case that a width or a height ofa luma coding block is greater than a predetermined specific value(e.g., 32, 64), as shown in FIG. 6, a TT split may be limited.

In the disclosure, the coding tree scheme may support that a luma andchroma block have a separate block tree structure. With respect to P andB slices, luma and chroma CTBs in a single CTU may be limited to havethe same coding tree structure. However, with respect to I slices, lumaand chroma blocks may have respective individual block tree structures.In the case that the individual block tree mode is applied, a luma CTBmay be partitioned into CUs based on a specific coding tree structure,and a chroma CTB may be partitioned into chroma CUs based on a differentcoding tree structure. This may mean that a CU in I slice may include acoding block of chroma component or coding blocks of two chromacomponent, and a CU in P or B slice may include blocks of three colorcomponents.

In the “Partitioning of the CTUs using a tree structure” describedabove, the quad-tree coding tree scheme with nested multi-type tree isdescribed, but a structure in which a CU is partitioned is not limitedthereto. For example, BT structure and TT structure may be interpretedas the concept included in the Multiple Partitioning Tree (MPT)structure, and it may be interpreted that a CU is partitioned through QTstructure and MPT structure. In an example that a CU is partitionedthrough QT structure and MPT structure, a syntax element includinginformation on the number of blocks to which a leaf node of QT structureis partitioned (e.g., MPT_split_type) and a syntax element includinginformation a direction to which a leaf node of QT structure ispartitioned between vertical and horizontal directions (e.g.,MPT_split_mode) may be signaled, and a split structure may bedetermined.

In another example, a CU may be partitioned in a method different fromQT structure, BT structure or TT structure. That is, different from thata CU of a lower layer depth is partitioned to ¼ size of a CU of a higherlayer depth according to QT structure, a CU of a lower layer depth ispartitioned to ½ size of a CU of a higher layer depth according to BTstructure, or a CU of a lower layer depth is partitioned to ¼ size or ½size of a CU of a higher layer depth according to TT structure, a CU ofa lower layer depth may be partitioned into ⅕, ⅓, ⅜, ⅗, ⅔ or ⅝ size of aCU of a higher layer depth in some cases, but a method of partitioning aCU is not limited thereto.

In the case that a portion of a tree node block exceeds a bottom orright picture boundary, the corresponding tree node block may be limitedthat all samples of all coded CUs are located within the pictureboundaries. In this case, for example, the following split rules may beapplied.

-   -   If a portion of a tree node block exceeds both the bottom and        the right picture boundaries,    -   If the block is a QT node and the size of the block is larger        than the minimum QT size, the block is forced to be split with        QT split mode.    -   Otherwise, the block is forced to be split with SPLIT_BT_HOR        mode    -   Otherwise if a portion of a tree node block exceeds the bottom        picture boundaries,    -   If the block is a QT node, and the size of the block is larger        than the minimum QT size, and the size of the block is larger        than the maximum BT size, the block is forced to be split with        QT split mode.    -   Otherwise, if the block is a QT node, and the size of the block        is larger than the minimum QT size and the size of the block is        smaller than or equal to the maximum BT size, the block is        forced to be split with QT split mode or SPLIT_BT_HOR mode.    -   Otherwise (the block is a BTT node or the size of the block is        smaller than or equal to the minimum QT size), the block is        forced to be split with SPLIT_BT_HOR mode.    -   Otherwise if a portion of a tree node block exceeds the right        picture boundaries,    -   If the block is a QT node, and the size of the block is larger        than the minimum QT size, and the size of the block is larger        than the maximum BT size, the block is forced to be split with        QT split mode.    -   Otherwise, if the block is a QT node, and the size of the block        is larger than the minimum QT size and the size of the block is        smaller than or equal to the maximum BT size, the block is        forced to be split with QT split mode or SPLIT_BT_VER mode.    -   Otherwise (the block is a BTT node or the size of the block is        smaller than or equal to the minimum QT size), the block is        forced to be split with SPLIT_BT_VER mode.

The quadtree coding block structure accompanying the multi-type tree mayprovide a very flexible block partitioning structure. Due to spittingtypes supported to the multi-type tree, different splitting patterns maypotentially cause the same coding block structure result in some cases.Generation of the redundant splitting patterns is limited to reduce adata mount of partitioning information. This will be described withreference to following drawings.

FIG. 7 is a diagram illustrating redundant partitioning patterns whichmay occur in binary-tree partitioning and ternary-tree partitioning asan embodiment to which the disclosure may be applied.

As illustrated in FIG. 7, two levels of consecutive binary splits in onedirection have the same coding block structure as binary splitting for acenter partition after the ternary splitting. In such a case, binarytree splitting (in the given direction) for the center partition of theternary tree splitting may be limited. The limitation may be applied toCUs of all pictures. When specific splitting is limited, signaling ofsyntax elements may be modified by reflecting such a limitation case andthe number of bits signaled for partitioning may be reduced through themodified signaling. For example, like the example illustrated in FIG. 7,when the binary tree splitting for the center partition of the CU islimited, a syntax element mtt_split_cu_binary_flag indicating whetherthe splitting is the binary splitting or the ternary splitting may notbe signaled and the value may be inferred as 0 by the decoder.

Prediction

In order to reconstruct a current processing unit in which decoding isperformed, decoded parts of a current picture or other picturesincluding the current processing unit may be used.

A picture using only the current picture for reconstruction, i.e.,performing the intra prediction may be referred to as an intra pictureor an I picture (slice), a picture (slice) using up to one motion vectorand reference index in order to predict each unit may be referred to asa predictive picture or P picture (slice), and a picture (slice) usingup to two motion vectors and reference indexes may be referred to as abi-predictive picture or B picture (slice).

The intra prediction means a prediction method that derives a currentprocessing block from a data element (e.g., a sample value, etc.) of thesame decoded picture (or slice). In other words, the intra predictionmeans a method for predicting a pixel value of the current processingblock by referring to reconstructed areas in the current picture.

Hereinafter, the inter prediction will be described in more detail.

Inter Prediction

The inter prediction means a prediction method of deriving the currentprocessing block based on data elements (e.g., the sample value ormotion vector) of pictures other than the current picture. In otherwords, the intra prediction means a method for predicting a pixel valueof the current processing block by referring to reconstructed areas inother reconstructed pictures other than the current picture.

The inter prediction (inter-picture prediction) as a technique foreliminating redundancy existing between pictures is mostly performed bymotion estimation and motion compensation.

In the disclosure, a detailed description of the inter prediction methoddescribed in FIGS. 1 and 2 above is made and the decoder may berepresented as an inter prediction based video/image decoding method ofFIG. 10 and an inter-prediction unit in the decoding apparatus of FIG.11 to be described below. Moreover, the encoder may be represented as aninter prediction based video/image encoding method of FIG. 8 and theinter-prediction unit in the encoding apparatus of FIG. 9 to bedescribed below. In addition, encoded data by FIGS. 8 and 9 may bestored in the form of a bitstream.

The prediction unit of the encoding apparatus/decoding apparatus mayderive the predicted sample by performing the inter prediction in unitsof the block. The inter prediction may represent prediction derived by amethod dependent to the data elements (e.g., sample values or motioninformation) of a picture(s) other than the current picture. When theinter prediction is applied to the current block, a predicted block(prediction sample array) for the current block may be derived based ona reference block (reference sample array) specified by the motionvector on the reference picture indicated by the reference pictureindex.

In this case, in order to reduce an amount of motion informationtransmitted in the inter-prediction mode, the motion information of thecurrent block may be predicted in units of a block, a subblock, or asample based on a correlation of the motion information between theneighboring block and the current block. The motion information mayinclude the motion vector and the reference picture index. The motioninformation may further include inter-prediction type (L0 prediction, L1prediction, Bi prediction, etc.) information.

In the case of applying the inter prediction, the neighboring block mayinclude a spatial neighboring block which is present in the currentpicture and a temporal neighboring block which is present in thereference picture. A reference picture including the reference block anda reference picture including the temporal neighboring block may be thesame as each other or different from each other. The temporalneighboring block may be referred to as a name such as a collocatedreference block, a collocated CU (colCU), etc., and the referencepicture including the temporal neighboring block may be referred to as acollocated picture (colPic). For example, a motion information candidatelist may be configured based on the neighboring blocks of the currentblock and a flag or index information indicating which candidate isselected (used) may be signaled in order to derive the motion vectorand/or reference picture index of the current block.

The inter prediction may be performed based on various prediction modesand for example, in the case of a skip mode and a merge mode, the motioninformation of the current block may be the same as the motioninformation of the selected neighboring block. In the case of the skipmode, the residual signal may not be transmitted unlike the merge mode.In the case of a motion vector prediction (MVP) mode, the motion vectorof the selected neighboring block may be used as a motion vectorpredictor and a motion vector difference may be signaled. In this case,the motion vector of the current block may be derived by using a sum ofthe motion vector predictor and the motion vector difference.

FIGS. 8 and 9 are diagrams illustrating an inter prediction basedvideo/image encoding method according to an embodiment of the disclosureand an inter prediction unit in an encoding apparatus according to anembodiment of the disclosure.

Referring to FIGS. 8 and 9, S801 may be performed by theinter-prediction unit 180 of the encoding apparatus and S802 may beperformed by the residual processing unit of the encoding apparatus.Specifically, S802 may be performed the subtraction unit 115 of theencoding apparatus. In S803, prediction information may be derived bythe inter-prediction unit 180 and encoded by the entropy encoding unit190. In S803, residual information may be derived by the residualprocessing unit and encoded by the entropy encoding unit 190. Theresidual information is information on the residual samples. Theresidual information may include information on quantized transformcoefficients for the residual samples.

As described above, the residual samples may be derived as transformcoefficients by the transform unit 120 of the encoding apparatus and thetransform coefficients may be derived as quantized transformcoefficients by the quantization unit 130. Information on the quantizedtransform coefficients may be encoded through a residual codingprocedure by the entropy encoding unit 190.

The encoding apparatus performs inter prediction for the current block(S801). The encoding apparatus may derive the inter prediction mode andthe motion information of the current block and generate predictedsamples of the current block. Here, an inter prediction mode determiningprocedure, a motion information deriving procedure, and a generationprocedure of the prediction samples may be simultaneously performed andany one procedure may be performed earlier than other procedures. Forexample, the inter-prediction unit 180 of the encoding apparatus mayinclude a prediction mode determination unit 181, a motion informationderivation unit 182, and a predicted sample derivation unit 183, and theprediction mode determination unit 181 may determine the prediction modefor the current block, the motion information derivation unit 182 mayderive the motion information of the current block, and the predictedsample derivation unit 183 may derive motion samples of the currentblock.

For example, the inter-prediction unit 180 of the encoding apparatus maysearch a block similar to the current block in a predetermined area(search area) of reference pictures through motion estimation and derivea reference block in which a difference from the current block isminimum or is equal to or less than a predetermined criterion. Areference picture index indicating a reference picture at which thereference block is positioned may be derived based thereon and a motionvector may be derived based on a difference in location between thereference block and the current block. The encoding apparatus maydetermine a mode applied to the current block among various predictionmodes. The encoding apparatus may compare RD cost for the variousprediction modes and determine an optimal prediction mode for thecurrent block.

For example, when the skip mode or the merge mode is applied to thecurrent block, the encoding apparatus may configure a merging candidatelist to be described below and derive a reference block in which adifference from the current block is minimum or is equal to or less thana predetermined criterion among reference blocks indicated by mergecandidates included in the merging candidate list. In this case, a mergecandidate associated with the derived reference block may be selectedand merge index information indicating the selected merge candidate maybe generated and signaled to the decoding apparatus. The motioninformation of the current block may be derived by using the motioninformation of the selected merge candidate.

As another example, when an (A)MVP mode is applied to the current block,the encoding apparatus may configure an (A)MVP candidate list to bedescribed below and use a motion vector of a selected mvp candidateamong motion vector predictor (mvp) candidates included in the (A)MVPcandidate list as the mvp of the current block. In this case, forexample, the motion vector indicating the reference block derived by themotion estimation may be used as the motion vector of the current blockand an mvp candidate having a motion vector with a smallest differencefrom the motion vector of the current block among the mvp candidates maybecome the selected mvp candidate. A motion vector difference (MVD)which is a difference obtained by subtracting the mvp from the motionvector of the current block may be derived. In this case, theinformation on the MVD may be signaled to the decoding apparatus.Further, when the (A)MVP mode is applied, the value of the referencepicture index may be configured as reference picture index informationand separately signaled to the decoding apparatus.

The encoding apparatus may derive the residual samples based on thepredicted samples (S802). The encoding apparatus may derive the residualsamples by comparing original samples of the current block and thepredicted samples.

The encoding apparatus encodes image information including predictioninformation and residual information (S803). The encoding apparatus mayoutput the encoded image information in the form of a bitstream. Theprediction information may include information on prediction modeinformation (e.g., skip flag, merge flag or mode index, etc.) andinformation on motion information as information related to theprediction procedure. The information on the motion information mayinclude candidate selection information (e.g., merge index, mvp flag ormvp index) which is information for deriving the motion vector. Further,the information on the motion information may include the information onthe MVD and/or the reference picture index information.

Further, the information on the motion information may includeinformation indicating whether to apply L0 prediction, L1 prediction, orbi-prediction. The residual information is information on the residualsamples. The residual information may include information on quantizedtransform coefficients for the residual samples.

An output bitstream may be stored in a (digital) storage medium andtransferred to the decoding apparatus or transferred to the decodingapparatus via the network.

Meanwhile, as described above, the encoding apparatus may generate areconstructed picture (including reconstructed samples and reconstructedblocks) based on the reference samples and the residual samples. This isto derive the same prediction result as that performed by the decodingapparatus, and as a result, coding efficiency may be increased.Accordingly, the encoding apparatus may store the reconstructed picture(or reconstructed samples or reconstructed blocks) in the memory andutilize the reconstructed picture as the reference picture. The in-loopfiltering procedure may be further applied to the reconstructed pictureas described above.

FIGS. 10 and 11 are diagrams illustrating an inter prediction basedvideo/image decoding method according to an embodiment of the disclosureand an inter prediction unit in a decoding apparatus according to anembodiment of the disclosure.

Referring to FIGS. 10 and 11, the decoding apparatus may perform anoperation corresponding to the operation performed by the encodingapparatus. The decoding apparatus may perform the prediction for thecurrent block based on received prediction information and derive theprediction samples.

S1001 to S1003 may be performed by the inter-prediction unit 260 of thedecoding apparatus and the residual information of S1004 may be obtainedfrom the bitstream by the entropy decoding unit 210 of the decodingapparatus. The residual processing unit of the decoding apparatus mayderive the residual samples for the current block based on the residualinformation. Specifically, the dequantization unit 220 of the residualprocessing unit may derive transform coefficients by performingdequantization based on quantized transform coefficients derived basedon the residual information and the inverse transform unit 230 of theresidual processing unit may derive the residual samples for the currentblock by performing inverse transform for the transform coefficients.S1005 may be performed by the addition unit 235 or the reconstructionunit of the decoding apparatus.

Specifically, the decoding apparatus may determine the prediction modefor the current block based on the received prediction information(S1001). The decoding apparatus may determine which inter predictionmode is applied to the current block based on the prediction modeinformation in the prediction information.

For example, it may be determined whether the merge mode or the (A)MVPmode is applied to the current block based on the merge flag.Alternatively, one of various inter prediction mode candidates may beselected based on the mode index. The inter prediction mode candidatesmay include a skip mode, a merge mode, and/or an (A)MVP mode or mayinclude various inter prediction modes to be described below.

The decoding apparatus derives the motion information of the currentblock based on the determined inter prediction mode (S1002). Forexample, when the skip mode or the merge mode is applied to the currentblock, the decoding apparatus may configure the merging candidate listto be described below and select one merge candidate among the mergecandidates included in the merging candidate list. The selection may beperformed based on the selection information (merge index). The motioninformation of the current block may be derived by using the motioninformation of the selected merge candidate. The motion information ofthe selected merge candidate may be used as the motion information ofthe current block.

As another example, when an (A)MVP mode is applied to the current block,the decoding apparatus may configure an (A)MVP candidate list to bedescribed below and use a motion vector of a selected mvp candidateamong motion vector predictor (mvp) candidates included in the (A)MVPcandidate list as the mvp of the current block. The selection may beperformed based on the selection information (mvp flag or mvp index). Inthis case, the MVD of the current block may be derived based on theinformation on the MVD, and the motion vector of the current block maybe derived based on the mvp of the current block and the MVD. Further,the reference picture index of the current block may be derived based onthe reference picture index information. The picture indicated by thereference picture index in the reference picture list for the currentblock may be derived as the reference picture referred for the interprediction of the current block.

Meanwhile, the motion information of the current block may be derivedwithout a candidate list configuration as described below and in thiscase, the motion information of the current block may be derivedaccording to a procedure disclosed in the prediction mode to bedescribed below. In this case, the candidate list configuration may beomitted.

The decoding apparatus may generate the predicted samples for thecurrent block based on the motion information of the current block(S1003). In this case, the reference picture may be derived based on thereference picture index of the current block and the predicted samplesof the current block may be derived by using the samples of thereference block indicated by the motion vector of the current block onthe reference picture. In this case, as described below, in some cases,a prediction sample filtering procedure for all or some of theprediction samples of the current block may be further performed.

For example, the inter-prediction unit 260 of the decoding apparatus mayinclude a prediction mode determination unit 261, a motion informationderivation unit 262, and a predicted sample derivation unit 263, and theprediction mode determination unit 261 may determine the prediction modefor the current block based on the received prediction mode information,the motion information derivation unit 262 may derive the motioninformation (the motion vector and/or reference picture index) of thecurrent block based on the information on the received motioninformation, and the predicted sample derivation unit 263 may derive thepredicted samples of the current block.

The decoding apparatus generates the residual samples for the currentblock based on the received residual information (S1004). The decodingapparatus may generate the reconstructed samples for the current blockbased on the predicted samples and the residual samples and generate thereconstructed picture based on the generated reconstructed samples(S1005). Thereafter, the in-loop filtering procedure may be furtherapplied to the reconstructed picture as described above.

As described above, the inter prediction procedure may include an interprediction mode determining step, a motion information deriving stepdepending on the determined prediction mode, and a prediction performing(predicted sample generating) step based on the derived motioninformation.

Determination of Inter Prediction Mode

Various inter prediction modes may be used for predicting the currentblock in the picture. For example, various modes including a merge mode,a skip mode, an MVP mode, an affine mode, and the like may be used. Adecoder side motion vector refinement (DMVR) mode, an adaptive motionvector resolution (AMVR) mode, etc., may be further used as an ancillarymode. The affine mode may be referred to as an affine motion predictionmode. The MVP mode may be referred to as an advanced motion vectorprediction (AMVP) mode.

The prediction mode information indicating the inter prediction mode ofthe current block may be signaled from the encoding apparatus to thedecoding apparatus. The prediction mode information may be included in abitstream and received by the decoding apparatus. The prediction modeinformation may include index information indicating one of multiplecandidate modes. Alternatively, the inter prediction mode may beindicated through a hierarchical signaling of flag information. In thiscase, the prediction mode information may include one or more flags.

For example, whether to apply the skip mode may be indicated bysignaling a skip flag, whether to apply the merge mode may be indicatedby signaling a merge flag when the skip mode is not applied, and it isindicated that the MVP mode is applied or a flag for additionaldistinguishing may be further signaled when the merge mode is notapplied. The affine mode may be signaled as an independent mode orsignaled as a dependent mode on the merge mode or the MVP mode. Forexample, the affine mode may be configured as one candidate of themerging candidate list or MVP candidate list as described below.

Derivation of Motion Information According to Inter Prediction Mode

The inter prediction may be performed by using the motion information ofthe current block. The encoding apparatus may derive optimal motioninformation for the current block through a motion estimation procedure.For example, the encoding apparatus may search a similar reference blockhaving a high correlation in units of a fractional pixel within apredetermined search range in the reference picture by using an originalblock in an original picture for the current block and derive the motioninformation through the searched reference block. The similarity of theblock may be derived based on a difference of phase based sample values.For example, the similarity of the block may be calculated based on anSAD between the current block (or a template of the current block) andthe reference block (or the template of the reference block). In thiscase, the motion information may be derived based on a reference blockhaving a smallest SAD in a search area. The derived motion informationmay be signaled to the decoding apparatus according to various methodsbased on the inter prediction mode.

Merge Mode and Skip Mode

FIG. 12 is a diagram for describing a neighboring block used in a mergemode or a skip mode as an embodiment to which the disclosure is applied.

When the merge mode is applied, the motion information of the currentprediction block is not directly transmitted and the motion informationof the current prediction block is derived by using the motioninformation of a neighboring prediction block. Accordingly, flaginformation indicating that the merge mode is used and a merge indexindicating which neighboring prediction block is used are transmitted toindicate the motion information of the current prediction block.

The encoder may search a merge candidate block used for deriving themotion information of the current prediction block in order to performthe merge mode. For example, up to five merge candidate blocks may beused, but the disclosure is not limited thereto. In addition, themaximum number of merge candidate blocks may be transmitted in a sliderheader (or tile group header) and the disclosure is not limited thereto.After finding the merge candidate blocks, the encoder may generate themerging candidate list and selects a merge candidate block having thesmallest cost among the merge candidate blocks as a final mergecandidate block.

The disclosure provides various embodiments for the merge candidateblock constituting the merging candidate list.

As the merging candidate list, for example, five merge candidate blocksmay be used. For example, four spatial merge candidates and one temporalmerge candidate may be used. As a specific example, in the case of thespatial merge candidate, the blocks illustrated in FIG. 12 may be usedas the spatial merge candidate.

FIG. 13 is a flowchart illustrating a method for configuring a mergingcandidate list according to an embodiment to which the disclosure isapplied.

Referring to FIG. 13, a coding apparatus (encoder/decoder) inserts thespatial merge candidates derived by searching the spatial neighboringblocks of the current block into the merging candidate list (S1301). Forexample, the spatial neighboring blocks may include a bottom left cornerneighboring block, a left neighbor bock, a top right corner neighboringblock, a top neighboring block, and a top left corner neighboring blockof the current block. However, this is an example and additionalneighboring blocks including a right neighboring block, a bottomneighboring block, a bottom right neighboring block, and the like may befurther used as the spatial neighboring blocks in addition to thespatial neighboring blocks. The coding apparatus may derive availableblocks by searching the spatial neighboring blocks based on a priorityand derive the motion information of the detected blocks as the spatialmerge candidates. For example, the encoder and decoder may search fiveblocks illustrated in FIG. 12 in the order of A1, B1, B0, A0, and B2 andsequentially index the available candidates and configure the indexedcandidates as the merging candidate list.

The coding apparatus inserts the temporal merge candidate derived bysearching the temporal neighboring block of the current block into themerging candidate list (S1302). The temporal neighboring block may bepositioned on the reference picture which is a different picture fromthe current picture at which the current block is positioned. Thereference picture at which the temporal neighboring block is positionedmay be referred to as a collocated picture or a col picture. Thetemporal neighboring block may be searched in the order of a bottomright corner neighboring block and a bottom right center block of aco-located block for the current block on the col picture.

Meanwhile, when motion data compression is applied, specific motioninformation may be stored as representative motion information in thecol picture for each predetermined storage unit. In this case, motioninformation for all blocks in the predetermined storage unit need not bestored, and as a result, a motion data compression effect may beobtained. In this case, the predetermined storage unit may bepredetermined for each 16×16 sample unit or 8×8 sample unit or sizeinformation for the predetermined storage unit may be signaled from theencoder to the decoder. When the motion data compression is applied, themotion information of the temporal neighboring block may be replacedwith the representative motion information of the predetermined storageunit at which the temporal neighboring block is positioned.

In other words, in this case, in terms of implementation, the temporalmerge candidate may be derived based on motion information of aprediction block covering a location subject to arithmetic right shiftand then arithmetic left shift by a predetermined value based on acoordinate (top left sample position) of the temporal neighboring blockother than a prediction block positioned on the coordinate of thetemporal neighboring block. For example, when the predetermined storageunit is a 2n×2n sample unit, if the coordinate of the temporalneighboring block is (xTnb, yTnb), motion information of a predictionblock positioned at ((xTnb>>n)<<n), (yTnb>>n)<<n)) which is a modifiedlocation may be used for the temporal merge candidate.

Specifically, for example, when the predetermined storage unit is a16×16 sample unit, if the coordinate of the temporal neighboring blockis (xTnb, yTnb), motion information of a prediction block positioned at((xTnb>>4)<<4), (yTnb>>4)<<4)) which is a modified location may be usedfor the temporal merge candidate. Alternatively, for example, when thepredetermined storage unit is an 8×8 sample unit, if the coordinate ofthe temporal neighboring block is (xTnb, yTnb), motion information of aprediction block positioned at ((xTnb>>3)<<3), (yTnb>>3)<<3)) which is amodified location may be used for the temporal merge candidate.

The coding apparatus may check whether the current number of mergecandidates is smaller than the maximum number of merge candidates(S1303). The maximum number of merge candidates may be predefined orsignaled from the encoder to the decoder. For example, the encoder maygenerate information on the maximum number of merge candidates andencode the generated information and transfer the encoded information tothe decoder in the form of a bitstream. When the maximum number of mergecandidates is completely filled, a subsequent candidate addition processmay not be performed.

As the checking result, when the current number of merge candidates issmaller than the maximum number of merge candidates, the codingapparatus inserts additional merge candidates into the merging candidatelist (S1304). The additional merge candidates may include, for example,ATMVP, a combined bi-predictive merge candidate (when a slice type ofcurrent slice is type B) and/or a zero-vector merge candidate.

As the checking result, when the current number of merge candidates isnot smaller than the maximum number of merge candidates, the codingapparatus may terminate the configuration of the merging candidate list.In this case, the encoder may select an optimal merge candidate amongthe merge candidates constituting the merging candidate list based onrate-distortion (RD) cost and signal selection information (e.g., mergeindex) indicating the selected merge candidate to the decoder. Thedecoder may select the optimal merge candidate based on the mergingcandidate list and the selection information.

The motion information of the selected merge candidate may be used asthe motion information of the current block and the predicted samples ofthe current block may be derived based on the motion information of thecurrent block as described above. The encoder may derive the residualsamples of the current block based on the predicted samples and signalthe residual information for the residual samples to the decoder. Thedecoder may generate the reconstructed samples based on the residualsamples derived based on the residual information and the predictedsamples and generate the reconstructed picture based on the generatedreconstructed samples as described above.

When the skip mode is applied, the motion information of the currentblock may be derived by the same method as the case where the merge modeis applied as above. However, when the skip mode is applied, a residualsignal for the corresponding block is omitted, and as a result, thepredicted samples may be directly used as the reconstructed samples.

MVP Mode

FIG. 14 is a flowchart illustrating a method for configuring a mergingcandidate list according to an embodiment to which the disclosure isapplied.

When the motion vector prediction (MVP) mode is applied, a motion vectorpredictor (mvp) candidate list may be generated by using the motionvector of the reconstructed spatial neighboring block (e.g., may be theneighboring block described in FIG. 12 above) and/or the motion vectorcorresponding to the temporal neighboring block (or Col block). In otherwords, the motion vector of the reconstructed spatial neighboring blockand/or the motion vector corresponding to the temporal neighboring blockmay be used as the motion vector predictor candidate.

The information on the prediction may include selection information(e.g., an MVP flag or MVP index) indicating an optimal motion vectorpredictor candidate selected among the motion vector predictorcandidates included in the list. In this case, the predictor may selectthe motion vector predictor of the current block among the motion vectorpredictor candidates included in the motion vector candidate list byusing the selected information. The predictor of the encoding apparatusmay obtain a motion vector difference (MVD) between the motion vectorand the motion vector predictor of the current block and encode theobtained MVD and output the encoded MVD in the form of the bitstream. Inother words, the MVD may be obtained by a value obtained by subtractingthe motion vector predictor from the motion vector of the current block.In this case, the predictor of the decoding apparatus may obtain themotion vector difference included in the information on the predictionand derive the motion vector of the current block by adding the motionvector difference and the motion vector predictor. The predictor of thedecoding apparatus may obtain or derive the reference picture indexindicating the reference picture from the information on the prediction.For example, the motion vector predictor candidate list may beconfigured as illustrated in FIG. 14.

Affine Motion Prediction

FIG. 15 illustrates an example of motion models according to anembodiment of the disclosure.

A conventional image compression technology (e.g., high efficiency videocoding (HEVC)) uses one motion vector in order to represent a motion ofa coding block. Although an optimum motion in a block unit may berepresented for each block in a method using one motion vector, theoptimum motion may not be actually an optimum motion of each pixel.Accordingly, if optimum motion vector is determined in a pixel unit,coding efficiency will be increased. Therefore, an embodiment of thedisclosure describes a motion prediction method of encoding or decodinga video signal using a multi-motion model. In particular, a motionvector may be represented in each pixel unit or subblock unit of a blockusing motion vectors at two to four control points. A prediction schemeusing such motion vectors of a plurality of control points may bedenoted as an affine motion prediction, an affine prediction, etc.

An affine motion model according to an embodiment of the disclosure mayrepresent four motion models, such as those illustrated in FIG. 15. Anaffine motion model that represents three motions (translation, scale,and rotate) among motions capable of representing the Affine motionmodel is denoted as a similarity (or simplified) affine motion model. Indescribing embodiments of the disclosure, the similarity (or simplified)affine motion model is basically described for convenience ofdescription, but the disclosure is not limited thereto.

FIG. 16 illustrates an example of a control point motion vector for anaffine motion prediction according to an embodiment of the disclosure.

As in FIG. 16, an affine motion prediction may determine motion vectorsat pixel positions (or subblocks) included in a block using a pair oftwo control point motion vectors (CPMV) v_0 and v_1. In this case, a setof the motion vectors may be denoted as an affine motion vector field(MVF). In this case, the affine motion vector field may be determinedusing Equation 1 below.

$\begin{matrix}\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}*x} - {\frac{\left( {v_{1y} - v_{0y}} \right)}{w}*y} + v_{0x}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{w}*x} - {\frac{\left( {v_{1x} - v_{0x}} \right)}{w}*y} + v_{0y}}}\end{matrix} \right. & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Equation 1, v_0 (v_0={v_0 x, v_0y}) indicates a motion vector CPMV0at a first control point at the top left position of a current block1300. v_1 (v_1={v_1x, v_1y}) indicates a motion vector CPMV1 at a secondcontrol point at the top right position of the current block 1300.Furthermore, w indicates the width of the current block 1300. v(v={v_x,v_y}) indicates a motion vector at a {x,y} position. A motion vector ina subblock (or pixel) unit may be derived using Equation 1. In anembodiment, motion vector precision may be rounded as 1/16 precision.

FIG. 17 illustrates an example of a motion vector for each subblock of ablock to which an affine motion prediction according to an embodiment ofthe disclosure has been applied.

Referring to FIG. 17, in a coding or decoding process, an affine motionvector field (MVF) may be determined in a pixel unit or block unit. Thatis, in an affine motion prediction, a motion vector of a current blockmay be derived in a pixel unit or a subblock unit. [223] If an affinemotion vector field is determined in the pixel unit, a motion vector maybe obtained based on each pixel value. If an affine motion vector fieldis determined in the block unit, a motion vector of a block may beobtained based on a center pixel value of the corresponding block. Inthe disclosure, as in FIG. 17, a case where an affine motion vectorfield (MVF) is determined in a 4*4 block unit is assumed. However, thisis for convenience of description and does not limit an embodiment ofthe disclosure. FIG. 17 illustrates an example of a case where a codingblock is composed of 16*16 samples and an affine motion vector field(MVF) is determined in a block unit of a 4*4 size.

An affine motion prediction may include an affine merge mode (orAF_MERGE) and an affine inter mode (or AF_INTER). The AF_INTER mode mayinclude an AF_4_INTER mode using a four-parameter-based motion model andan AF_6_INTER mode using a six-parameter-based motion model.

Affine Merge Mode

AF_MERGE determines control point motion vector (CPMV)s according to theaffine motion model of the neighbouring block coded as the affine motionprediction. An affine coded neighbouring block in a search order may beused for AF_MERGE. A current block can be coded as AF_MERGE when one ormore of the neighbouring blocks are coded as affine motion prediction.

That is, if the affine merge mode is applied, CPMVs of a current blockmay be derived using CPMVs of a neighboring block. In this case, theCPMVs of the neighboring block may be used as the CPMVs of the currentblock without any change. The CPMVs of the neighboring block aremodified based on the size of the neighboring block and the size of thecurrent block and may be used as the CPMVs of the current block.

FIG. 18 illustrates an example of neighboring blocks used in an affinemotion prediction in an affine merge mode according to an embodiment ofthe disclosure.

In the affine merge (AF_MERGE) mode, the encoder may perform encoding asin the following process.

Step-1: Scan neighboring blocks A to E 1810, 1820, 1830, 1840, and 1850of a current coding block 1800 in the alphabetical sequence. A blockfirst coded in the affine prediction mode according to the scanningsequence is determined as a candidate block of affine merge (AF_MERGE)

Step-2: Determine an affine motion model using a control point motionvector (CPMV) of a determined candidate block

Step-3: Determine a control point motion vector (CPMV) of the currentblock 1800 according to the affine motion model of the candidate block,and determine the MVF of the current block 1800.

FIG. 19 illustrates an example in which a block on which an affinemotion prediction is performed using neighboring blocks to which anaffine motion prediction according to an embodiment of the disclosurehas been applied.

For example, as in FIG. 19, if a block A 1920 is coded in an affinemode, after the block A 1920 is determined as a candidate block, anaffine motion model may be derived using control point motion vectors(CPMV) (e.g., v2 and v3) of the block A 1920, and control point motionvectors (CPMV) v0 and v1 of a current block 1900 may be determined. Theaffine motion vector field (MVF) of the current block 1900 may bedetermined based on the control point motion vectors (CPMV) of thecurrent block 1900, and encoding may be performed.

FIG. 20 is a diagram for describing a method of generating a mergecandidate list using peripheral affine coding blocks according to anembodiment of the disclosure.

Referring to FIG. 20, if a CPMV pair is determined using an affine mergecandidate, candidates, such as those illustrated in FIG. 20, may beused. In FIG. 20, a case where the scan sequence of a candidate list isset as A, B, C, D, and E is assumed. However, the disclosure is notlimited thereto, and the scan sequence may be previously set in varioussequences.

In an embodiment, if the number of candidates (hereinafter may bedenoted as affine candidates) coded in an affine mode (or affineprediction) available in neighboring blocks (i.e., A, B, C, D, and E) is0, an affine merge mode of a current block may be skipped. If the numberof available affine candidates is one (e.g., A), a motion model of acorresponding candidate may be used to derive control point motionvectors CPMV_0 and CPMV_1 of a current block. In this case, an indexindicative of the corresponding candidate may not be necessary (orcoded). If the number of available affine candidates is two or more, twocandidates in the scanning sequence may be configured as a candidatelist for AF_MERGE. In this case, candidate selection information, suchas an index indicative of a candidate selected within the candidatelist, may be signaled. The selection information may be a flag or indexinformation, and may be denoted as AF_MERGE_flag, AF_merge_idx, etc.

In an embodiment of the disclosure, motion compensation for the currentblock may be performed based on a size of a sub-block. In this case, asub-block size of the affine block (current block) is derived. If bothwidth and height of the sub-block are larger than 4 luma samples, amotion vectors for each sub-block is derived and DCT-IF based motioncompensation ( 1/16 pel for luma and 1/32 for chroma) can be invoked forthe sub-block. Otherwise, enhanced bi-linear interpolation filter basedmotion compensation is invoked for the whole affine block.

In an embodiment of the disclosure, when merge/skip flag is true andboth width and height for the CU are larger than or equal to 8, anaffine flag in CU level is signalled in the bitstream to indicatewhether affine merge mode is used. And when the CU is coded as AF_MERGE,the merge candidate index with maximum value 5 is signalled forspecifying which motion information candidate in the affine mergecandidate list is used for the CUA

FIGS. 21 and 22 are diagrams for describing a method of configuring anaffine merge candidate list using a neighboring block encoded by anaffine prediction according to an embodiment of the disclosure.

Referring to FIG. 21, the affine merge candidate list is constructed asfollowing steps.

1) Insert Model Based Affine Candidates

Model based affine candidate means that the candidate is derived fromthe valid neighbor reconstructed block coded in the affine mode. Asshown in FIG. 21, the scan order for the candidate block is from left(A), above (b), above right (C), left bottom (D) to above left (E).

If the neighbour left bottom block A is coded in 6-parameter affinemode, the motion vectors v_4, v_5, and v_6 of the top left corner, aboveright corner and left bottom corner of the CU which contains the block Aare obtained. And the motion vectors v0, v_1, and v_2 of the top leftcorner on the current CU is calculated according to v_4, v_5, and v_6 by6-parameter affine model.

If the neighbour left bottom block A is coded in 4-parameter affinemode, the motion vectors v_4 and v_5 of the top left corner and aboveright corner of the CU which contains the block A are obtained. And themotion vectors v_0 and v_1 of the top left corner on the current CU iscalculated according to v_4 and v_5 by 4-parameter affine model.

2) Insert Control Point Based Affine Candidates

Referring to FIG. 21, control points based candidate means the candidateis constructed by combining the neighbor motion information of eachcontrol point.

The motion information for the control points is derived firstly fromthe specified spatial neighbors and temporal neighbor shown in FIG. 21.CP_k (k=1, 2, 3, 4) represents the k-th control point. A, B, C, D, E, Fand G are spatial positions for predicting CP_k (k=1, 2, 3); H istemporal position for predicting CP4.

The coordinates of CP_1, CP_2, CP_3 and CP_4 is (0, 0), (W, 0), (H, 0)and (W, H), respectively, where W and H are the width and height ofcurrent block.

The motion information of each control point is obtained according tothe following priority order.

For CP_1, the checking priority is A→B→C, A is used if it is available.Otherwise, if B is available, B is used. If both A and B areunavailable, C is used. If all the three candidates are unavailable, themotion information of CP1 cannot be obtained.

For CP_2, the checking priority is E→D;

For CP_3, the checking priority is G→F;

For CP_4, H is used.

Secondly, the combinations of controls points are used to construct themotion model.

Motion vectors of two control points are needed to compute the transformparameters in 4-parameter affine model. The two control points can beselected from one of the following six combinations ({CP_1, CP_4},{CP_2, CP_3}, {CP_1, CP_2}, {CP_2, CP_4}, {CP_1, CP_3}, {CP_3, CP_4}).For example, use the CP_1 and CP_2 control points to construct4-parameter affine motion model, denoted as Affine (CP_1, CP_2).

Motion vectors of three control points are needed to compute thetransform parameters in 6-parameter affine model. The three controlpoints can be selected from one of the following four combinations({CP_1, CP_2, CP_4}, {CP_1, CP_2, CP_3}, {CP_2, CP_3, CP_4}, {CP_1,CP_3, CP_4}). For example, use CP_1, CP_2 and CPv3 control points toconstruct 6-parameter affine motion model, denoted as Affine (CP_1,CP_2, CP_3).

Also, in an embodiment of the disclosure, in the affine merge mode, ifthe affine merge candidate exists, it can be always considered assix-parameter affine mode.

Affine Inter Mode

FIG. 23 illustrates an example of neighboring blocks used in an affinemotion prediction in an affine inter mode according to an embodiment ofthe disclosure.

Referring to FIG. 23, an affine motion prediction may include an affinemerge mode (or AF_MERGE) and an affine inter mode (or AF_INTER). In theaffine inter mode (AF_INTER), after two control point motion vectorprediction (CPMVP) and CPMV are determined, a control point motionvector difference CPMVD corresponding to a difference may be transmittedfrom the encoder to the decoder. A detained process of encoding theaffine inter mode AF_INTER may be as follows.

Step-1: Determine two CPMVP pair candidates

Step-1.1: Determine a maximum of twelfth CPMVP candidate combinations(refer to Equation 2 below){(v ₀ ,v ₁ ,v ₂)|v ₀ ={v _(A) ,v _(B) ,v _(C) },v ₁ ={v _(D) ,v _(E) },v₂ ={v _(F) ,v _(G)}}  [Equation 2]

In Equation 2, v_0 indicates a motion vector CPMV0 at a top left controlpoint 2310 of a current block 2300. v_1 indicates a motion vector CPMV1at the top right control point 2311 of the current block 2300. v_2indicates a motion vector CPMV2 at the bottom left control point 2312 ofthe current block 2300. v_A indicates the motion vector of a neighboringblock A 2320 neighboring the top left of the top left control point 2310of the current block 2300. v_B indicates the motion vector of aneighboring block B 2322 neighboring the top of the top left controlpoint 2310 of the current block 2300. vC indicates the motion vector ofa neighboring block C 2324 neighboring the left of the top left controlpoint 2310 of the current block 2300, v_D indicates the motion vector ofa neighboring block D 2326 neighboring the top of the top right controlpoint 2311 of the current block 2300. v_E indicates the motion vector ofa neighboring block E 2328 neighboring the top right of the top rightcontrol point 2311 of the current block 2300. v_F indicates the motionvector of a neighboring block F 2330 neighboring the left of the bottomleft control point 2312 of the current block 2300. v_G indicates themotion vector of a neighboring block G 2332 neighboring the left of thebottom left control point 2312 of the current block 2300.

Step-1.2: Use top two candidates sorted based on a smaller differencevalue (DV) in a CPMVP candidate combination (refer to Equation 3 below)DV=|(v _(1x) −v _(0x))*h−(v _(2y) −v _(0y))*w|+|(v _(1y) −v _(0y))*h+(v_(2x) −v _(0x))*w|  [Equation 3]

v_0x indicates the x-axis element of the motion vector V0 or CPMV0 atthe top left control point 2310 of the current block 2300. v_1xindicates the x-axis element of the motion vector V1 or CPMV1 at the topright control point 2311 of the current block 2300. v_2x indicates thex-axis element of the motion vector V_2 or CPMV2 at the bottom leftcontrol point 2312 of the current block 2300. v_0y indicates the y-axiselement of the motion vector V_0 or CPMV_0 at the top left control point2310 of the current block 2300. v_1y indicates the y-axis element of themotion vector V_1 or CPMV_1 at the top right control point 2311 of thecurrent block 2300. v_2 y indicates the y-axis element of the motionvector V_2 or CPMV_2 at the bottom left control point 2312 of thecurrent block 2300. w indicates the width of the current block 2300. hindicates the height of the current block 2300.

Step-2: Use an AMVP candidate list when a control point motion vectorpredictor (CPMVP) pair candidate is smaller than 2

Step-3: Determine a control point motion vector predictor (CPMVP) ofeach of two candidates, and optimally selects a candidate and CPMVhaving a smaller value as by comparing RD costs

Step-4: Transmit an index corresponding to the optimum candidate and acontrol point motion vector difference (CPMVD)

In an embodiment of the disclosure, in AF_INTER, the constructionprocess of the CPMVP candidate is provided. Same as AMVP, the number ofcandidate is two and the index indicating the position of candidate listis signaled.

The construction process of a CPMVP candidate list is as follows:

1) Scan the neighbouring blocks to check whether it is coded as theaffine motion prediction or not. If the scanned block is coded as theaffine prediction, derive the motion vector pair of current block fromthe affine motion model of the scanned neighbouring block until thenumber of candidate is two.

2) If the number of candidate is less than two, perform the candidateconstruction process. Also, in an embodiment of the disclosure, afour-parameter (two-control-point) affine inter mode is used to predictthe content with the motion model of zoom-in/out and rotation. As shownin FIG. 16, the affine motion field of the block is described bytwo-control-point motion vectors.

The motion vector field (MVF) of a block is described by the previouslydescribed equation 1.

In the prior art, the advanced motion vector prediction (AMVP) modeneeds to signal a motion vector prediction (MVP) index and motion vectordifferences (MVDs). When the AMVP mode is applied in this disclosure, anaffine_flag is signaled to indicate whether the affine prediction isused. If the affine prediction is applied, the syntax of inter_dir,ref_idx, mvp_index, and two MVDs (mvd_x and mvd_y) are signaled. Anaffine MVP pair candidate list containing two affine MVP pairs isgenerated. The signaled mvp_index is used to select one of them. Theaffine MVP pair is generated by two kinds of affine MVP candidates. Oneis the spatial inherited affine candidate, and the other is the cornerderived affine candidate. If the neighbor CUs are coded in the affinemode, the spatial inherited affine candidates can be generated. Theaffine motion model of the neighbor affine coded block is used togenerate the motion vectors of the two-control point MVP pair. The MVsof the two-control point MVP pair of the spatial inherited affinecandidate are derived by using the following equations.V _(0x) =V _(B0x)+(V _(B2_x) −V_(B0x))*(posCurCU_Y−posRefCU_Y)/RefCU_height+(V _(Bix) −V_(B0x))*(posCurCU_X−posRefCU_X)/RefCU_width  [Equation 4]V _(0y) =V _(B0y)+(V _(B2_y) −V_(B0y))*(posCurCU_Y−posRefCU_Y)/RefCU_height+(V _(B1y) −V_(B0y))*(posCurCU_X−posRefCU_X)/RefCU_width  [Equation 5]

Where V_B0, V_B1, and V_B2 can be replaced by the top-left MV, top-rightMV, and bottom-left MV of any reference/neighbor CU, (posCurCU_X,posCurCU_Y) is the position of the top-left sample of the current CUrelative to the top-left sample of the frame, (posRefCU_X, posRefCU_Y)is the position of the top-left sample of the reference/neighbor CUrelative to the top-left sample of the frame.V _(1x) =V _(B0x)+(B _(B1x) −V _(B0x))*CU_width/RefCU_width  [Equation6]V _(1y) =V _(B0y)+(V _(B1y) −V _(B0y))*CU_width/RefCU_width  [Equation7]

FIG. 24 illustrates an example of neighboring blocks used for an affinemotion prediction in the affine inter mode according to an embodiment ofthe disclosure.

Referring to FIG. 24, if the number of the MVP pairs is smaller than 2,the corner derived affine candidate is used. The neighbor motionvectors, as shown in FIG. 24, are used to derive the affine MVP pair.For the first corner derived affine candidate, the first available MV inset A (A0, A1, and A2) and first available MV in set B (B0 and B1) areused to construct the first MVP pair. For the second corner derivedaffine candidate, the first available MV in set A and first available MVin set C (C0 and C1) are used to calculate the MV of top-right controlpoint. The first available MV in set A and the calculated top-rightcontrol point MV are the second MVP pair.

In an embodiment of the disclosure, two candidate sets with two (three)candidates {mv_0, mv_1} ({mv_0, mv_1, mv_2) are used to predict two(three) control points of the affine motion model. Given motion vectordifference vectors, mvd_0, mvd_1, mvd_2, the control points arecalculated by using the following equations.mv ₀ =mv ₀ +mvd ₀mv ₁ =mv ₁ +mvd ₁ +mvd ₀mv ₂ =mv ₂ +mvd ₂ +mvd ₀  [Equation 8]

FIGS. 25 and 26 are diagrams illustrating a method of deriving motionvector candidates using motion information of neighboring blocks in theaffine inter mode according to an embodiment of the disclosure.

The affine candidate list is appended sequentially by extending affinemotion from spatial neighboring blocks (extrapolated affine candidates),the combination of motion vectors from spatial neighboring blocks(virtual affine candidates) and HEVC motion vector prediction (MVP)candidates until there are two affine MVPs in the candidate list. Thecandidate sets are constructed as follows:

1. Up to two different affine MV predictor sets are derived from affinemotion of the neighboring blocks. Neighboring blocks A0, A1, B0, B1, andB2 as shown in FIG. 25 are checked. If the neighboring block is codedusing affine motion model and its reference frame is same as thereference frame of the current block, MVs at two (for 4-parameter affinemodel) or three (for 6-parameter affine model) control points of thecurrent block are derived from the affine model of this neighbor.

2. FIG. 29 shows the neighboring blocks used to generate the virtualaffine candidate set. The neighboring MVs are divided into three groups:S_0={mv_A, mv_B, mv_C}, S_1={mv_D, mv_E} and S_2={mv_F, mv_G}. mv_0 isthe first MV in S0 that refers to the same reference picture as thecurrent block; mv_1 is the first MV in S1 that refers to the samereference picture of the current block; and mv_2 is the first in S2 thatrefers to the same reference picture of the current block.

If only mv_0 and mv_1 can be found, mv_2 is derived as by using thefollowing equation.

$\begin{matrix}{{{\overset{\_}{mv}}_{2}^{x} = {{\overset{\_}{mv}}_{0}^{x} - {h\frac{\left( {{\overset{\_}{mv}}_{1}^{y} - {\overset{\_}{mv}}_{0}^{y}} \right)}{w}}}},{{\overset{\_}{mv}}_{2}^{y} = {{\overset{\_}{mv}}_{0}^{y} + {h\frac{\left( {{\overset{\_}{mv}}_{1}^{x} - {\overset{\_}{mv}}_{0}^{x}} \right)}{w}}}},} & \left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack\end{matrix}$

Referring to Equation 9, the current block size is W×H.

If only mv_0 and mv_2 can be found, mv_1 is derived by using thefollowing equation.

$\begin{matrix}{{{\overset{\_}{mv}}_{1}^{x} = {{\overset{\_}{mv}}_{0}^{x} + {h\frac{\left( {{\overset{\_}{mv}}_{2}^{y} - {\overset{\_}{mv}}_{0}^{y}} \right)}{w}}}},{{\overset{\_}{mv}}_{1}^{y} = {{\overset{\_}{mv}}_{0}^{y} - {h{\frac{\left( {{\overset{\_}{mv}}_{2}^{x} - {\overset{\_}{mv}}_{0}^{x}} \right)}{w}.}}}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

In an embodiment of the disclosure, Affine inter may be performedaccording to the following sequence.

-   -   Input: affine motion parameters, reference picture samples    -   Output: prediction block of a CU    -   Process    -   Derive sub-block size of the affine block    -   If both width and height of the sub-block are larger than 4 luma        samples,    -   For each sub-block    -   Derive the motion vector for the sub-block.    -   DCT-IF based motion compensation ( 1/16 pel for luma and 1/32        for chroma) is invoked for the sub-block    -   Otherwise, enhanced bi-linear interpolation filter based motion        compensation is invoked for the whole affine block

Also, in an embodiment of the disclosure, when merge/skip flag is falseand both width and height for the CU are larger than or equal to 8, anaffine flag in CU level is signalled in the bitstream to indicatewhether affine inter mode is used. And when the CU is coded as affineinter mode, a model flag is signalled for specifying whether 4-parameteror 6-parameter affine model is used for this CU. If the model flag istrue, AF_6_INTER mode (6-parameter affine model) is applied and 3 MVDswill be parsed; otherwise, AF_6_INTER mode (4-parameter affine model) isapplied and 2 MVDs will be parsed.

In AF_4_INTER mode, similar to affine merge mode, affine motion vectorpairs extrapolated from neighbour blocks coded in the affine mode areconstructed and insert into candidate list firstly.

After that, if the size of the candidate list is smaller than 4,candidates with motion vector pair {(v_0,v_1)|v0={v_A,v_B,v_c},v_1={v_D, v_E}} is constructed using the neighbourblocks. As shown in FIG. 22, v_0 is selected from the motion vectors ofthe block A, B or C. The motion vector from the neighbour block isscaled according to the reference list and the relationship among thePOC of the reference for the neighbour block, the POC of the referencefor the current CU and the POC of the current CU. And the approach toselect v_1 from the neighbour block D and E is similar. When thecandidate list is larger than 4, the candidates are firstly sortedaccording to the consistency of the neighbouring motion vectors(similarity of the two motion vectors in a pair candidate) and only thefirst four candidates are kept.

If the number of candidate list is smaller than 4, the list is padded bythe motion vector pair composed by duplicating each of the AMVPcandidates.

In AF_6_INTER mode, similar to affine merge mode, affine motion vectortriples extrapolated from neighbour blocks coded in the affine mode areconstructed and insert into candidate list firstly.

After that, if the size of the candidate list is smaller than 4,candidates with motion vector triples {(v_0, v_1, v_2)|v0={v_A, v_B,v_c}, v1={v_D, v_E}, v2={v_G, v_H}} is constructed using the neighbourblocks. As shown in FIG. 22, v_0 is selected from the motion vectors ofthe block A, B or C. The motion vector from the neighbour block isscaled according to the reference list and the relationship among thePOC of the reference for the neighbour block, the POC of the referencefor the current CU and the POC of the current CU. And the approach toselect v_1 from the neighbour block D and E, and select v_2 from F and Gis similar. When the candidate list is larger than 4, the candidates arefirstly sorted according to the consistency of the neighbouring motionvectors (similarity of the two motion vectors in a triple candidate) andonly the first four candidates are kept.

If the number of candidate list is smaller than 4, the list is padded bythe motion vector triple composed by duplicating each of the AMVPcandidates.

After the CPMV of the current CU are derived, according to the number ofaffine parameters, the MVF of the current CU is generated according tothe following Equation 11 for 4-parameter affine model, and according tothe following Equation 12 for 6-parameters affine model.

$\begin{matrix}\left\{ \begin{matrix}{v_{x} = {{\frac{v_{1x} - v_{0x}}{W}x} - {\frac{v_{1y} - v_{0y}}{W}y} + v_{0x}}} \\{v_{y} = {{\frac{v_{1y} - v_{0y}}{W}x} - {\frac{v_{1x} - v_{0x}}{W}y} + v_{0y}}}\end{matrix} \right. & \left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack \\\left\{ \begin{matrix}{v_{x} = {{\frac{v_{1x} - v_{0x}}{W}x} - {\frac{v_{2x} - v_{0x}}{H}y} + v_{0x}}} \\{v_{y} = {{\frac{v_{1y} - v_{0y}}{W}x} - {\frac{v_{2y} - v_{0y}}{H}y} + v_{0y}}}\end{matrix} \right. & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

The sub-block size MXN is derived as in the following Equation 13, whereMvPre is the motion vector fraction accuracy ( 1/16).

$\begin{matrix}\left\{ {\begin{matrix}{M = {{clip}\; 3\left( {4,w,\frac{w \times {MvPre}}{\max\left( {{{abs}\left( {v_{1x} - v_{0x}} \right)},{{abs}\left( {v_{1y} - v_{0y}} \right)}} \right)}} \right)}} \\{N = {{clip}\; 3\left( {4,h,\frac{h \times {MvPre}}{\max\left( {{{abs}\left( {v_{2x} - v_{0x}} \right)},{{abs}\left( {v_{2y} - v_{0y}} \right)}} \right)}} \right)}}\end{matrix}\quad} \right. & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

After derived by Equation 12, M and N should be adjusted downward ifnecessary to make it a divisor of w and h, respectively. If M or N issmaller than 8, WIF is applied; otherwise, sub-block based affine motioncompensation is applied.

FIG. 27 illustrates an example of a method of deriving an affine motionvector field in a subblock unit according to an embodiment of thedisclosure.

Referring to FIG. 27, to derive motion vector of each M×N sub-block, themotion vector of the center sample of each sub-block, as shown in FIG.27, is calculated according to Equation 11 or Equation 12, and roundedto 1/16 fraction accuracy. Then the SHVC upsampling interpolationfilters are applied to generate the prediction of each sub-block withderived motion vector.

SHVC upsampling interpolation filters, which have same filter length andnormalization factor as HEVC motion compensation interpolation filters,are used as motion compensation interpolation filters for the additionalfractional pel positions. The chroma component motion vector accuracy is1/32 sample, the additional interpolation filters of 1/32 pel fractionalpositions are derived by using the average of the filters of the twoneighbouring 1/16 pel fractional positions.

AF_MERGE mode is selected at the encoder-side in the similar way asconventional merge mode selection is performed. The candidate list isconstructed firstly, and minimum RD-cost inside the candidates isselected to compare with RD-cost of other inter modes. Result of thiscomparison is a decision whether AF_MERGE is applied or not.

For AF_4_INTER mode, a RD cost check is used to determine which motionvector pair candidate is selected as the control point motion vectorprediction (CPMVP) of the current CU. After the CPMVP of the currentaffine CU is determined, affine motion estimation is applied and thecontrol point motion vector (CPMV) is found. Then the difference of theCPMV and the CPMVP is decided.

In encoder side, AF_6_INTER mode will only be verified when AF_MERGE orAF_4_INTER mode is selected as the best mode in the previous modeselected stage.

In an embodiment of the disclosure, affine inter (affine AMVP) mode canbe performed as below:

1) AFFINE_MERGE_IMPROVE: instead of finding the first neighboring blockin the affine mode, the improvement tries to find the neighboring blockwith the largest coding unit size as the affine merge candidate.

2) AFFINE_AMVP_IMPROVE: add the neighboring blocks in the affine mode tothe affine AMVP candidate list similar to the traditional AMVP process.

The detailed affine AMVP candidate list construction process is asfollows.

First, the below left neighboring block is checked whether it is usingthe affine motion model and has the reference index with the currentreference index. If it does not exist, the left neighboring block isthen checked in the same way. If it does not exist, the below leftneighboring block is checked whether it is using the affine motion modeland with the different reference index. If it exists, the scaled affinemotion vector is added to the reference picture list. If it does notexist, the left neighboring block with be checked in the same way. [330]Second, the above right neighboring block, the above neighboring block,and above left neighboring block will then be checked in the same way.

If we have found two candidates after the above processes, we will havefinished constructing the affine AMVP candidate lists. If we have notfound two candidates, the original process in the JEM software will beperformed to construct the affine AMVP candidate lists.

3) AFFINE_SIX_PARAM: besides the four-parameter affine motion model,six-parameter affine motion model is also added as an additional model.

The six parameter affine motion model is derived by using the followingequation.

$\begin{matrix}\left\{ \begin{matrix}{{MV_{x}} = {{ax} + {by} + c}} \\{{MV_{y}} = {{dx} + {ey} + f}}\end{matrix} \right. & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$

Since there are six-parameters in the above motion model, three motionvectors in the above left position MV_0, the above right position MV_1,and the bottom left position MV_2 are needed to determine the model. Thethree motion vectors are determined in a similar way as the two motionvectors in the four-parameter affine motion model. Note that the affinemodel merge is always set as the six-parameter affine motion model.

4) AFFINE_CLIP_REMOVE: delete the motion vector constraints for all theaffine motion vectors. Let the motion compensation process handle themotion vector constraints themselves.

Affine Motion Model

As described above, various affine motion models may be used orconsidered in the Affine inter prediction. For example, the Affinemotion model may represent four motions as in FIG. 15. An affine motionmodel that represents three motions (translation, scale, and rotate),among motions capable of representing the Affine motion model, may becalled a similarity (or simplified) affine motion model. The number ofCPMVs derived depending on which one of the affine motion models is usedand/or a method of deriving a sample/subblock unit MV of a current blockmay be different.

motion model can be used. In AF_INTER, a six-parameter motion model isproposed to use in addition to the existing a four parameter motionmodel in JEM. The six-parameter affine motion model is described in thefollowing Equation 15.x′=a*x+b*y+cy′=d*x+e*y+f  [Equation 15]

Here, the coefficients a, b, c, d, e, and f are the affine motionparameters and, (x,y) and (x′,y′) are the co-ordinates of pixel locationbefore and after the transformation of the affine motion model. To usethe affine motion model in video coding, if CPMV0, CPMV1 and CPMV2 arethe MV for CP0 (left above), CP1 (right above) and CP2 (left bottom),Equation 16 can be described as:

$\begin{matrix}\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}*x} + {\frac{\left( {v_{2x} - v_{0x}} \right)}{h}*y} + v_{0x}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{w}*x} - {\frac{\left( {v_{2y} - v_{0y}} \right)}{h}*y} + v_{0y}}}\end{matrix} \right. & \left\lbrack {{Equation}\mspace{14mu} 16} \right\rbrack\end{matrix}$

where CPMV_0={v_0x,v_0y}, CPMV_1={v_1x,v_1y}, CPMV_2={v_2 x,v_2y}, and wand h are the width and the height of coding block, respectively.Equation 16 describes the motion vector field (MVF) of a block.

A flag is parsed at the CU level to indicate whether the four-parameteror the six-parameter affine motion model is used when the neighboringblocks are coded as the affine prediction. If no neighboring block iscoded as the affine prediction, the flag is skipped and four-parametermodel is used for the affine prediction. In other words, thesix-parameter model is considered in the condition that one or more ofthe neighboring blocks are coded as the affine motion model. When itcomes to the number of CPMVD, two and three CPMVDs are signaled for thefour-parameter and six-parameter affine motion model, respectively.[345] Also, in an embodiment of the disclosure, pattern-matched motionvector refinement can be used. In the pattern-matched motion vectorderivation (named PMMVD in JEM encoder description, shortened to PMVD inthis document) of JEM, the decoder needs to evaluate several motionvector (MV) candidates to determine a starting MV candidate for CU-levelsearch. In sub-CU-level search, in addition to the best CU-level MV,several MV candidates are added. The decoder needs to evaluate these MVcandidates to find the best MV, which requires a lot of memorybandwidth. In the proposed pattern-matched motion vector refinement(PMVR), the concepts of template matching and bilateral matching in PMVDin JEM are adopted. One PMVR_flag is signaled when skip mode or mergemode is selected to indicate PMVR is enabled or not. To reduce thememory bandwidth requirement significantly in comparison with PMVD, a MVcandidate list is generated, and a starting MV candidate index isexplicitly signaled if PMVR is applied.

The candidate list is generated by using merge candidate list generationprocess, but the sub-CU merge candidates, e.g., the affine candidatesand ATMVP candidates, are excluded. For bilateral matching, only theuni-prediction MV candidate is included. A bi-prediction MV candidate isdivided into two uni-prediction MV candidates. Also, similar MVcandidates (MV differences smaller than a predefined threshold) are alsoremoved. For the CU-level search, a diamond search MV refinement isperformed starting from the signaled MV candidate.

The sub-CU-level search is only enabled for the bilateral matching mergemode. To reduce memory bandwidth, only the MV determined from theCU-level search is evaluated. The search window of the sub-CU-levelsearch for all sub-CUs is the same as the search window of the CU-levelsearch. Therefore, no additional bandwidth is required for sub-CU-levelsearch.

The template matching is also used to refine the MVP in AMVP mode. InAMVP mode, two MVPs are generated by using HEVC MVP generation process,and one MVP index is signaled to select one of them. The selected MVP isfurther refined by using template matching in PMVR. If the adaptivemotion vector resolution (AMVR) is applied, the MVP is rounded to thecorresponding precision before template matching refinement. Thisrefinement process is named as pattern-matched motion vector predictorrefinement (PMVPR). In the rest of this document, if not particularlyspecified, PMVR includes template matching PMVR, bilateral matchingPMVR, and PMVPR.

To reduce the memory bandwidth requirement, the PMVR is disabled for4×4, 4×8, and 8×4 CUs. To further reduce the memory bandwidthrequirement, the search range of {template matching, bilateral matching}for CU area equal to 64 is reduced to {±2, ±4}, and the search range of{template matching, bilateral matching} for CU area larger than 64 isreduced to {±6, ±8}. By using all the above methods described in thisPMVR section, the required memory bandwidth is reduced from 45.9× inPMVD of JEM-7.0 to 3.1× in PMVR, compared to the worst case in HEVC.

Application Technology when Affine is Used in a Non-QT Block

FIG. 28 illustrates a method of generating a prediction block and amotion vector in an inter prediction to which an affine motion modelaccording to an embodiment of the disclosure has been applied.

FIG. 28 shows an equation for deriving a motion vector if an affinemotion model is applied. The motion vector may be derived based on thefollowing equation 17.V _(x)=(1−a)x−by−e(V _(x) ,V _(y))=(x−x′,y−y′)V _(y) =−cx+(1−d)y−f  [Equation 17]

In this case, v_x indicates the x component of a sample unit motionvector of an (x, y) coordinate sample within a current block. v_yindicates the y component of the sample unit motion vector of the (x, y)coordinate sample within the current block. That is, (v_x, v_y) becomessample unit motion vectors of the (x, y) coordinate sample. In thiscase, a, b, c, d, e, and f indicate parameters of an equation forderiving the sample unit motion vectors of the (x, y) coordinates fromthe control points (CP) of the current block. The CP may be representedas a control pixel. The parameters may be derived from motioninformation of CPs of each PU transmitted in a PU unit. The equation forderiving the sample unit motion vectors derived from the motioninformation of the CPs may be applied to each sample of a block, and maybe derived as the position of the sample within a reference image basedon the x-axis and y-axis relative position of each sample. The sampleunit motion vector may be differently derived depending on the size,asymmetrical or symmetrical, block position, etc. of a block in aQTBT(TT) block partition structure, and a detailed embodiment thereof isillustrated through FIGS. 29 to 38.

FIG. 29 is a diagram illustrating a method of performing a motioncompensation based on a motion vector of a control point according to anembodiment of the disclosure.

Referring to FIG. 29, a case where a current block is an 2N×2N block isassumed and described. For example, a motion vector of a top left samplewithin the current block may be said to be v_0. Furthermore, the motionvectors of CPs may be said to be v_1 and v_2 using, as CPs, the samplesof neighboring blocks neighboring the current block. That is, assumingthat the width and height of the current block are S and coordinates atthe top left sample position of the current block are (xp, yp), thecoordinates of CP0 among the CPs may be said to be (xp, yp), thecoordinates of CP1 may be said to be (xp+S, yp), and the coordinates ofCP2 may be said to be (xp, yp+S). The motion vector of the CP0 may besaid to be v_0, the motion vector of the CP1 may be said to be v_1, andthe motion vector of the CP2 may be said to be v_2. A sample unit motionvector may be derived using the motion vectors of the CPs. The sampleunit motion vector may be derived based on the following equation 18.

$\begin{matrix}{{V_{x} = {{\frac{V_{x_{1}} - V_{x_{0}}}{S}x} - {\frac{V_{x_{2}} - V_{x_{0}}}{S}y} + V_{x_{0}}}}{V_{y} = {{\frac{V_{y_{1}} - V_{y_{0}}}{S}x} - {\frac{V_{y_{2}} - V_{y_{0}}}{S}y} + V_{y_{0}}}}} & \left\lbrack {{Equation}\mspace{14mu} 18} \right\rbrack\end{matrix}$

In this case, v_x and v_y indicate the x component and y component of amotion vector for a sample at (x, y) coordinates within the currentblock, respectively. v_x0 and v_y0 indicate the x component and ycomponent of a motion vector v_0 for the CP0, respectively. v_x1 andv_y1 indicate the x component and y component of a motion vector v_1 forthe CP1, respectively. v_x2 and v_y2 indicate the x component and ycomponent of a motion vector v_2 for the CP2. The motion vectors ofsamples within the current block may be derived based on relativepositions within the current block according to an equation for derivinga sample unit motion vector, such as Equation 18.

FIG. 30 is a diagram illustrating a method of performing a motioncompensation based on motion vectors of control points in a nonregularblock according to an embodiment of the disclosure.

FIG. 30 illustrates the CPs of a block partitioned into N×2N. Anequation for deriving a sample unit motion vector within a current blockmay be driven using the same method as that of the partitioning type2N×2N. In a process of deriving the equation, a width value suitable fora shape of the current block may be used. In order to derive the sampleunit motion vector, three CPs may be derived. The positions of the CPsmay be adjusted as in FIG. 30. That is, assuming that the width andheight of a current block are S/2 and S and the coordinates of thecurrent block at the top left sample position are (xp, yp), thecoordinates of CP0 of the CPs may be (xp, yp), the coordinates of CP1thereof may be (xp+S/2, yp), and the coordinates of CP2 may be (xp,yp+S). The sample unit motion vector may be derived based on thefollowing equation 19.

$\begin{matrix}{{V_{x} = {{\frac{2\left( {V_{x_{1}} - V_{x_{0}}} \right)}{S}x} - {\frac{V_{x_{2}} - V_{x_{0}}}{S}y} + V_{x_{0}}}}{V_{y} = {{\frac{2\left( {V_{y_{1}} - V_{y_{0}}} \right)}{S}x} - {\frac{V_{y_{2}} - V_{y_{0}}}{S}y} + V_{y_{0}}}}} & \left\lbrack {{Equation}\mspace{14mu} 19} \right\rbrack\end{matrix}$

In this case, vx and vy indicate the x component and y component of amotion vector for a sample at (x, y) coordinates within the currentblock, respectively. v_x0 and v_y0 indicate the x component and ycomponent of a motion vector v_0 for the CP0, respectively. v_x1 andv_y1 indicate the x component and y component of a motion vector v_1 forthe CP1, respectively. v_x2 and v_y2 indicate the x component and ycomponent of a motion vector v_2 for the CP2, respectively. Equation 3indicates an equation for deriving a sample unit motion vector in whichthe width of the current block is considered to be S/2. The motionvectors of samples within the current block partitioned from a CU basedon the partitioning type N×2N may be derived based on relative positionswithin the current block according to an equation for deriving a sampleunit motion vector, such as Equation 19.

FIG. 31 is a diagram illustrating a method of performing a motioncompensation based on motion vectors of control points in a nonregularblock according to an embodiment of the disclosure.

FIG. 31 illustrates blocks partitioned based on the partitioning type2N×N. In order to derive a sample unit motion vector, three CPs may bederived. The height of a current block may be adjusted to S/2 based on ashape of the current block shown in FIG. 31 by adjusting the positionsof the CPs as in FIG. 31. That is, assuming that the width and height ofthe current block are S and S/2 and the coordinates of the current blockat the top left sample position are (xp, yp), the coordinates of CP0among the CPs may be (xp, yp), the coordinates of CP1 may be (xp+S, yp),and the coordinates of CP2 may be (xp, yp+S/2). A sample unit motionvector may be derived based on the following equation 20.

$\begin{matrix}{{V_{x} = {{\frac{V_{x_{1}} - V_{x_{0}}}{S}x} - {\frac{2\left( {V_{x_{2}} - V_{x_{0}}} \right)}{S}y} + V_{x_{0}}}}{V_{y} = {{\frac{V_{y_{1}} - V_{y_{0}}}{S}x} - {\frac{2\left( {V_{y_{2}} - V_{y_{0}}} \right)}{S}y} + V_{y_{0}}}}} & \left\lbrack {{Equation}\mspace{14mu} 20} \right\rbrack\end{matrix}$

In this case, v_x and v_y indicate the x component and y component of amotion vector for a sample at (x, y) coordinates within the currentblock, respectively. v_x0 and v_y0 indicate the x component and ycomponent of a motion vector v_0 for the CP0, respectively. v_x1 andv_y1 indicate the x component and y component of a motion vector v_1 forthe CP1, respectively. v_x2 and v_y2 indicate the x component and ycomponent of a motion vector v_2 for the CP2, respectively. Equation 4indicates an equation for deriving a sample unit motion vector in whichthe height of the current block has been considered to be S/2. Motionvectors of each sample within a current block partitioned from a CUbased on the partitioning type 2N×N may be derived based on relativepositions within the current block according to an equation for derivinga sample unit motion vector, such as Equation 4.18.

FIGS. 32 to 38 are diagrams illustrating a method of performing a motioncompensation based on motion vectors of control points in a nonregularblock according to an embodiment of the disclosure.

FIG. 32 illustrates the CPs of asymmetrical current blocks. Asillustrated in FIG. 32, the width and height of the asymmetrical currentblocks may be said to be W and H. In order to derive a sample unitmotion vector, three CPs of each current block may be derived. Thecoordinates of the CPs may be adjusted based on a width and height basedon a shape of a current block as in FIG. 32. That is, assuming that thewidth and height of the current block is W and H and the coordinates ofeach current block at a top left sample position are (xp, yp), thecoordinates of CP0 among the CPs may be set as (xp, yp), the coordinatesof CP1 may be set as (xp+W, yp), and the coordinates of CP2 may be setas (xp, yp+H). In this case, a sample unit motion vector within thecurrent block may be derived based on the following equation 21.

$\begin{matrix}{{V_{x} = {{\frac{V_{x_{1}} - V_{x_{0}}}{W}x} - {\frac{V_{x_{2}} - V_{x_{0}}}{H}y} + V_{x_{0}}}}{V_{y} = {{\frac{V_{y_{1}} - V_{y_{0}}}{W}x} - {\frac{V_{y_{2}} - V_{y_{0}}}{H}y} + V_{y_{0}}}}} & \left\lbrack {{Equation}\mspace{14mu} 21} \right\rbrack\end{matrix}$

In this case, v_x and v_y indicate the x component and y component of amotion vector for a sample at (x, y) coordinates within the currentblock, respectively. v_x0 and v_y0 indicate the x component and ycomponent of a motion vector v_0 for the CP0, respectively. v_x1 andv_y1 indicate the x component and y component of a motion vector v_1 forthe CP1, respectively. v_x2 and v_y2 indicate the x component and ycomponent of a motion vector v_2 for the CP2. Equation 21 indicates anequation for deriving a sample unit motion vector in which the width andheight of asymmetrical current blocks have been considered.

Meanwhile, according to the disclosure, in order to reduce the amount ofdata for motion information of CPs indicated in a block unit, motioninformation prediction candidates for at least one CP may be selectedbased on motion information of a neighboring block or a neighbor samplefor a current block. The motion information prediction candidate may becalled an affine motion information candidate or an affine motion vectorcandidate. The affine motion information candidates may include thecontents disclosed with reference to FIGS. 33 to 38, for example.

MVD Coding

The current state-of-the art video coding standard uses motion vectorsand its motion vector predictors to generate motion vector differences(MVD). The MVD can be more formally defined as the difference betweenthe motion vector and the motion vector predictor. Similar to the motionvector, the MVD has an x 0 and y component that correspond to the motionin x (horizontal) and y (vertical) directions. The MVD is an attributethat is available only when the coding unit is encoded using the(Advanced) Motion Vector Prediction ((A)MVP) mode.

Once the MVD is determined, it is then encoded using entropy techniques.The video standards rely on using MVDs as one of its possible ways toexploit the redundancy in motion vectors and to achieve compression. Atthe decoder, the motion vector difference (MVD) is decoded before themotion vectors of the coding unit are decoded. Encoding MVD overencoding the actual motion vectors serves to exploit the redundancybetween the motion vectors and its predictors and in so doing enhancethe compression efficiency. The input to the MVD coding stage at thedecoder is just the coded MVD bins that have been parsed for decoding.The inputs to the MVD coding stage at the encoder are the actual MVDvalues and additionally a flag (“imv” flag) that indicates theresolution for the MVD encoding. The flag is used to decide if the MVDshould be expressed as 1-pel (or pixel), 4-pel or as quarter-pel.

FIG. 39 illustrates an overall coding structure for deriving a motionvector according to an embodiment of the disclosure.

Referring to FIG. 39, the coding unit is initially checked if it is theMerge Mode (S3901).

If the coding unit is in Merge mode, an affine flag and merge index areparsed to proceed with the decoding (S3902).

If the coding unit is not in Merge mode, it then exists in the AMVPmode. In the AMVP mode, the list information is first parsed, i.e., ifList 0 or List 1 or both the lists are to be used (S3903).

Then, the affine flag is parsed (S3904). Following this, the parsedAffine flag is checked if it is true or false (S3905).

If true, then parse_MVD_LT and parse_MVD_RT corresponding to the left(LT) and right (RT) MVDs are processed (S3906). If the Affine flag isfalse, then the MVD is processed (S3907). Affine motion modeling in thespecial case of AMVP will be described in detail below.

FIG. 40 shows an example of an MVD coding structure according to anembodiment of the disclosure.

Referring to FIG. 40, first and foremost, the MVD greater than zeroflags for the horizontal (MVDxGT0) and vertical (MVDYGT0) components areparsed (S4001).

Following this, the parsed data for the horizontal component is checkedif it's greater than zero (i.e., MVDxGT0) (S4002). If the MVDxGT0 flagis true (i.e. MVDxGT0 is equal to ‘1’), then the horizontal componentgreater than one is parsed (i.e., MVDxGT1) (S4002). If the MVDxGT0 isnot true (i.e. MVDxGT0 is equal to ‘0’), then the MVDxGT1 data is notparsed.

A similar procedure is then followed for the vertical component (S4003,S4004).

Following this, the parsed MVD data can be processed further in theblocks labelled MVDx_Rem_Level and MVDy_Rem_Level in order to obtain thereconstructed MVDs (S4005, S4006).

FIG. 41 shows an example of an MVD coding structure according to anembodiment of the disclosure.

FIG. 41 illustrates how the decoder processes the data in the blockMVDx_Rem_Level in FIG. 40 further so as to decode the MVDx component. Ifthe decoded flag indicating that the parsed data would be greater thanzero (i.e., MVDxGT0) is true (S4101) and the decoded flag indicating theparsed data would be greater than one (i.e., MVDxGT1) is true (S4102),then the bins corresponding to the parsed MVDx component are decodedusing Exponential Golomb (EG) Code with order one (S4103). The inputs tothe EG would be the bins containing the absolute min two (i.e., Abs-2)MVD values and the Golomb order of one.

The sign information is then parsed by decoding the bypass bincontaining the information (S4104). If the decoded bypass bin has avalue of 1, then a negative sign is appended to the decoded MVDx. Ifhowever, the decoded bypass bin has a value of 0, then the decoded MVDis indicated as a positive value. If MVDxGR0 is true but the MVDxGR1 isnot true, then this indicates that the absolute value of the MVDx beingdecoded is 1. The sign information is then parsed and updated. However,if the MVDxGR0 is false, then the reconstructed MVDx is 0.

A similar process is used to decode the MVDy (i.e., MVDy_Rem_Level) atthe decoder is shown in the FIG. 42 below.

FIG. 42 shows an example of an MVD coding structure according to anembodiment of the disclosure.

Referring to FIG. 42, if the decoded flag indicating that the parsedMVDy greater than zero (i.e., MVDyGT0) is true (S4201), then the flagMVDyGR1 is checked (S4202).

If both MVDyGR0 and MVDyGR1 are true, then the parsed MVD data isdecoded using EG Code with inputs being the bins containing the absoluteminus two (Abs-2) MVD and order one (S4203). Following this, the signinformation is parsed and decoded to obtain the decoded MVDy (S4204). IfMVDyGR0 is true but MVDyGR1 is false then, the absolute vertical valueis considered to be either +1/−1. The sign information is then parsed ina similar manner as explained above and decoded, so as to obtain thedecoded MVDy. If the MVDyGR0 flag is false, MVDy is zero.

FIG. 43 shows an example of an MVD coding structure according to anembodiment of the disclosure.

Referring to FIG. 43, at the encoder the signed MVD values are to beencoded. Similar to the FIG. 41, the greater than zero bins are encodedfor the x and y components (S4301, S4311), i.e., MVDxGR0 and MVDyGR0 bychecking the absolute values of the horizontal and vertical components.Then the greater than one flags are encoded for the horizontal andvertical components (S4302, S4312), i.e., MVDxGR1 and MVDyGR1. Followingthis the absolute MVD values are encoded similar to the decoder, thehorizontal and vertical components are encoded sequentially.

For the horizontal MVD encoding, if the absolute horizontal MVDcomponent is greater zero (i.e., MVDxGR0) and if it is greater than one(i.e., MVDxGR1), then the (absolute value −2) is encoded using the EGCode with order one (S4303). Following this the sign information isencoded using bypass bin (S4304). If MVDxGR0 was true and MVDxGR1 wasnot true, then just the sign information is encoded. If MVDxGR0 is nottrue, then the MVDx is zero. The same process is repeated to encode MVDy(S4313, S4314).

Affine Coding

Prior video coding standards have only considered translational motionmodel. However, the underlying motion may incorporate effects such aszooming, rotation, panning and other irregular motions. In order tocapture this nature of motion, the latest video coding standardintroduced Affine motion coding, where by the irregular characteristicsof the motion information can be captured using either a 4-parameter ora 6-parameter Affine motion model.

If a 4 parameter model is used, then 2 control points are generated andif the 6-parameter model is used 3 control points are used. FIG. 16,previously described, illustrates the concept of affine motion moreclearly. By using the 4-parameter model, the current block is encodedusing two control point motion vectors given by v_0 (cpmv_0) and v1(cpmv_1).

Once these control points are derived, the MVF for each of the 4×4sub-blocks is described by the following equation 22.

$\begin{matrix}\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}x} - {\frac{\left( {v_{1y} - v_{0y}} \right)}{w}y} + v_{0x}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{w}x} + {\frac{\left( {v_{1x} - v_{0x}} \right)}{w}y} + v_{0y}}}\end{matrix} \right. & \left\lbrack {{Equation}\mspace{14mu} 22} \right\rbrack\end{matrix}$

Where (v_0x, v_0 y) is motion vector of the top-left corner controlpoint, and (v_1x, v_1y) is motion vector of the top-right corner controlpoint. The motion vector of each 4×4 sub-block is calculated by derivingthe motion vector of the center sample of each sub-block as illustratedin the FIG. 27, previously described.

Embodiment 1

In an embodiment of the disclosure, there is proposed a method forutilizing the correlation between motion vector differences (MVDs) ofcontrol points and removing redundancy by coding some control pointsbased on differences between control points.

In the disclosure, for convenience of description, a case where anaffine motion model using four parameters is applied, that is, a casewhere the upper left and upper right control points are used for affinemotion prediction, is mainly described, but the disclosure is limitedthereto. Even when a motion model using six parameters is applied, orwhen three or more control points are used through other cases, thedifference transmission method between MVDs proposed in the disclosuremay be applied in substantially the same/similar manner.

That is, in the embodiment of the disclosure, the encoder/decoder mayuse the correlation between the upper left and upper right controlpoints and redundancy between MVDs by coding any one control point(e.g., the upper right control point) using the MVD difference betweenthe upper left and upper right control points.

According to an embodiment, the decoder may restore (or derive) the MVDof the upper right control point by decoding the MVD of the upper leftcontrol point according to a conventional MVD coding method, decodingthe difference between the MVDs of the upper left and upper rightcontrol points to the MVD of the upper left control point, and addingthe difference between the MVDs of the upper left and upper rightcontrol points to the MVD of the upper left control point.

According to the disclosure, the MVD difference between the upper leftcontrol point and the upper right control point may be shortly referredto as an MVD difference (or difference MVD), but the disclosure is notlimited thereto.

FIG. 44 is a view illustrating a method for deriving affine motionvector difference information according to an embodiment of thedisclosure.

Referring to FIG. 44, the following description focuses primarily on adecoder for convenience of description, but the disclosure is notlimited thereto, and the method of signaling MVD information accordingto an embodiment of the disclosure may be performed in an encoder and adecoder in substantially the same manner. Although it is described abovein connection with FIG. 44 that two control points at the upper left andupper right sides are used for affine prediction, the disclosure is notlimited thereto. For example, although three control points at the lowerleft, upper left, and upper right sides are used, the same may beapplied likewise.

According to an embodiment of the disclosure, the encoder/decoder mayencode/decode the MVD of the upper right control point using thedifference between the MVDs of the upper left and upper right controlpoints.

The decoder identifies whether affine prediction (or affine motionprediction) is applied to the current block (S4401). When affineprediction is not applied to the current block, the decoder parses theMVD of the current block (S4402).

When affine prediction is applied to the current block, the decoderparses the MVD difference flag (S4403) and identifies whether the MVDdifference is used in the current block based on the MVD difference flag(S4404). If the MVD difference is not used in the current block, thedecoder parses the MVDs for the upper left and upper right controlpoints in the same way as conventional (S4405).

When the MVD difference is used in the current block, the decoder parsesthe MVD of the upper left control point and parses the MVD difference(S4406). The decoder may restore (or derive or obtain) the MVD of theupper right control point by adding the MVD difference to the MVD of theupper left control point.

In one embodiment, a syntax element may be transmitted through a bitstream to achieve the proposed method. For example, a flag (or syntaxelement), e.g., is_delta_affine_MVD, indicating that the MVD differencehas been used (or whether the MVD difference is activated) may betransmitted through the bit stream. Further, a flag (or syntax element)that is used at a slice, coding tree unit, or coding unit level andindicates whether the MVD difference is used in a corresponding levelunit may be transmitted from the encoder to the decoder. Table 2 belowshows possible use of a high-level syntax in a bit stream when the MVDdifference flag is used.

TABLE 2 high_level_parameter_set( ) { Description ... is_delta_affine_MVD u (1) ...

In Table 2, when is_delta_affine_MVD is 1, it indicates thatis_delta_affine_MVD is present in a slice header of a non-IDR picture ofa coded video sequence (CVS). When is_delta_affine_MVD is 0, itindicates that is_delta_affine_MVD does not exist in the slice headerand that the adaptive difference MVD according to the present embodimentis not used in CVS.

Further, in an embodiment, a syntax element for indicating whether thedifference MVD according to the present embodiment is applied at aslice, coding tree unit, or coding unit level may be additionallysignaled. For example, a syntax structure according to Table 3 below maybe defined.

TABLE 3 slice_segment_header( ) { Description ... if(is_delta_affine_MVD)   slice_delta_mvd u (1) ... } ...

In Table 3, if slice_delta_mvd is 0, it indicates that the current CU(or current slice) does not use the MVD difference (or MVD differencefunction), and if slice_delta_mvd is 1, it indicates that the CU usesthe MVD difference. Further, in Table 6, it is assumed that a syntaxelement indicating whether to apply the MVD difference is included inthe slice segment header, but the disclosure is not limited thereto andmay be included in syntax of various levels. For example, a syntaxelement indicating whether to apply the MVD difference may be includedin the coding tree unit syntax and the coding unit syntax.

Further, in another embodiment, the MVD difference may always be applied(or used) without signaling whether to use.

Embodiment 2

In an embodiment of the disclosure, a method for determining whether touse the MVD difference based on a threshold is proposed to control theuse of the MVD difference technique. This ensures a higher level ofcorrelation between the upper left MVD and the upper right MVD prior toapplying the proposed method, thereby increasing the flexibility andfurther enhancing the accuracy of the first embodiment described above.As an example, the threshold may be determined in various ways. Forexample, the threshold may adopt an empirical value or may be derivedfrom basic data statistics. An example in which the threshold is used isdescribed below with reference to the drawings.

FIG. 45 is a view illustrating a method for deriving motion vectordifference information based on a threshold according to an embodimentof the disclosure.

Referring to FIG. 45, the following description focuses primarily on adecoder for convenience of description, but the disclosure is notlimited thereto, and the method of signaling MVD information accordingto an embodiment of the disclosure may be performed in an encoder and adecoder in substantially the same manner. Although it is described abovein connection with 45 that two control points at the upper left andupper right sides are used for affine prediction, the disclosure is notlimited thereto. For example, although three control points at the lowerleft, upper left, and upper right sides are used, the same may beapplied likewise.

According to an embodiment of the disclosure, the encoder/decoder mayencode/decode the MVD of the upper right control point using thedifference between the MVDs of the upper left and upper right controlpoints and, in this case, a threshold may be used.

The decoder identifies whether affine prediction (or affine motionprediction) is applied to the current block (S4501). When affineprediction is not applied to the current block, the decoder parses theMVD of the current block (S4502).

When affine prediction is applied to the current block, the decoderparses the MVD difference flag (S4503) and identifies whether the MVDdifference is used in the current block based on the MVD difference flag(S4504). If the MVD difference is not used in the current block, thedecoder parses the MVDs for the upper left and upper right controlpoints in the same way as conventional (S4505).

When the MVD difference is used in the current block, the decoder parsesthe threshold (S4506). The decoder parses the MVD of the upper leftcontrol point based on the parsed threshold and parses the MVDdifference (S4507). The decoder may restore (or derive or obtain) theMVD of the upper right control point by adding the MVD difference to theMVD of the upper left control point.

In one embodiment, the threshold may be used to compare a differencebetween the MVDs of the upper left control point and the upper rightcontrol point. That is, when the difference between the MVDs of theupper left control point and the upper right control point is greaterthan the threshold, the proposed MVD difference method may not beapplied. If the difference between the MVDs of the upper left controlpoint and the upper right control point is less than or equal to thethreshold, the MVD difference method may be applied.

A different threshold may be set per picture, slice, CTU, or CU. In thiscase, the threshold may be transmitted in each header, or may beextended and transmitted in another header. Alternatively, the thresholdmay be kept fixed. In this case, syntax parsing or additional overheadsignaling may not be required.

Embodiment 3

In an embodiment of the disclosure, other context models andbinarization methods may be additionally applied to the above-describedembodiments. That is, in the above-described embodiments 1 and 2, sincethe upper-right control point is coded based on a difference between theMVDs of the upper-left and upper-right control points, it isadvantageous that it does not share the same context model with theupper left control point in performing entropy coding on MVDx_GR0,MVDy_GR0, and MVDx_GR1 and MVDy_GR1 flags. This is because there is ahigh possibility that the default probability of MVD is different fromthe probability obtained from coding on the upper right control point byusing the difference MVD.

Here, MVDx_GR0 and MVDy_GR0 are flags indicating whether the horizontaland vertical components, respectively, of the MVD are greater than 0.MVDx_GR1 and MVDy_GR1 are flags indicating whether the horizontal andvertical components, respectively, of the MVD are greater than 1.

Accordingly, in an embodiment of the disclosure, the encoder/decoder mayuse different context models in performing entropy coding on syntaxelements indicating MVD information for the upper right control pointand the upper left control point. Further, in an embodiment, differentbinarization techniques for syntax elements indicating MVD informationfor the upper right control point and the upper left control point maybe used to enhance compression performance.

Embodiment 4

In an embodiment of the disclosure, there is proposed a vector codingtechnique for jointly coding the MVDs of upper left and upper rightcontrol points for each of horizontal and vertical components. Thisembodiment independently derives the correlation between the upper leftand upper right control points of the horizontal and vertical componentsby data statistics.

FIG. 46 is a view illustrating a vector coding method for an affinemotion vector difference according to an embodiment of the disclosure.

FIG. 46 is derived from data statistics using frequency analysis.Although it is described above in connection with FIG. 46 that twocontrol points at the upper left and upper right sides are used foraffine prediction, the disclosure is not limited thereto. For example,although three control points at the lower left, upper left, and upperright sides are used, the same may be applied likewise. Further, in FIG.46, a method for performing vector coding on the MVD of the horizontalcomponent (i.e., the x-axis component) is described, and the same may beapplied to the MVD of the vertical component (i.e., the y-axiscomponent).

As an example, the MVD horizontal components on the upper left and upperright sides may be displaced and distributed in an elliptical shape asillustrated in FIG. 46. Here, the center point in the position (0, 0)which is not shaded indicates that the MVD horizontal components of theupper left and upper right control points correspond to 0. The centerpoint corresponds to a MVD combination that occurs most frequently inthe data set. FIG. 46 may be regarded as a grid having positive andnegative MVD values.

Further, a block adjacent to the center point means an increase ordecrease in MVD value at a single control point or both control points.Frequency analysis of data suggests that certain groups of MVD valuesoccur with similar probabilities. That is, blocks illustrated in thesame pattern in FIG. 46 may be classified into one group, and MVD valueswithin each group may be generated with similar probabilities accordingto data frequency analysis.

Consequently, in the disclosure, a layer representing an MVD combination(or group) having a similar probability of occurrence is defined. In oneembodiment, four layers may be defined as illustrated in FIG. 46. Inanother embodiment, it may be extended to incorporate several differentlayers. However, according to data analysis, it may be identified thatmost of the data may be processed by the layers illustrated in 46.

FIG. 47 is a view illustrating a vector coding method for an affinemotion vector difference according to an embodiment of the disclosure.

Referring to FIG. 47, two layers as described above in connection withFIG. 46 are shown as an example. An unshaded first layer and a shadedsecond layer are shown.

The first layer includes a center point of the (0,0) position, and thesecond layer includes some of the coordinates adjacent to the centerpoint.

Referring to FIGS. 46 and 47, the MVD value generally increases as eachconcentric circle (i.e., layer) increases. As described above, thevertical component of MVD also exhibits the same characteristics. Dataanalysis suggests that there is a high correlation between the affineMVDs of the upper left and upper right control points, which may bejointly used.

The method described above in connection with FIG. 39 may be applied tothe coding structure according to an embodiment of the disclosure.Referring back to FIG. 39 described above, in step S3907, the decoderdoes not individually parse the MVD of the upper left control point andthe MVD of the upper right control point, but parses the MVDs of theupper left and upper right control points together (or simultaneously).

In an embodiment, whether to use (or apply) a vector coding scheme maybe activated/deactivated through a flag syntax. In this case, thedecoder may perform an additional check to determine whether the CUshould be coded in the vector coding mode.

FIG. 48 is a parsing flowchart for MVD components according to anembodiment of the disclosure.

Referring to FIG. 48, the encoder/decoder encodes/decodes the level forthe horizontal component of the upper left and upper right control pointMVDs (S4801) and encodes/decodes the level of the vertical component ofthe upper left and upper right control point MVDs. (S4802). That is, theencoder/decoder may parse the MVDs of the upper left and upper rightcontrol points together (or simultaneously).

As an embodiment, the encoder/decoder may determine (or derive) finalMVD horizontal/vertical components by obtaining layer information forthe horizontal/vertical components and then encoding/decoding indexinformation indicating specific coordinates in the layer.

FIG. 49 is a view illustrating a coding structure of a motion vectordifference performed based on vector coding according to an embodimentof the disclosure.

Referring to FIG. 49, the following description focuses primarily on adecoder for convenience of description, but the disclosure is notlimited thereto, and the method of signaling affine motion vectordifference information according to an embodiment of the disclosure maybe performed in an encoder and a decoder in substantially the samemanner.

In an embodiment of the disclosure, MVDs for upper left and upper rightcontrol points may be coded together based on vector coding. In FIG. 49,a method for performing vector coding on the MVD of the horizontalcomponent (i.e., the x-axis component) is described, and the same may beapplied to the MVD of the vertical component (i.e., the y-axiscomponent). FIG. 49 corresponds to the MVDx_LT_MVDx_RT_Vector_Levelanalysis step of step S4801 of FIG. 48.

The decoder parses a flag (i.e., Layer_(x)_GT0) indicating whether thelayer of the horizontal components of the MVDs of the upper left andupper right control points is larger than layer 0 (i.e., the firstlayer) (S4901). The layer 0 indicates a layer including the center pointof the (0,0) position. If the flag is false, all of the horizontalcomponents of the control points correspond to 0, and in this case, thedecoder performs an MVDy_LT_MVDy_RT_Vector_Level analysis step (i.e.,S4802 in FIG. 48).

If Layer_(x_)GT0 is true, the decoder parses a first index indicating abin coded with two contexts (S4902 and S4903). The first index maydetermine (i) whether the target MVDx combination is in layer 1 (i.e.,the second layer), and if so, which index it corresponds to in thecorresponding layer, or (ii) whether the decoding needs to perform aprocess for checking a subsequent layer (S4904). For example, the firstindex may have the results of {(0,0), (0,1), (1,0), (1,1)}. If the firstindex value is (0,0), it indicates that the target MVD combination doesnot exist in the current layer and a subsequent layer need be checked.The remaining three combinations represent index values indicatingspecific coordinates within the layer.

That is, if the first index value is not (0, 0), the MVD horizontalcomponents of the upper left and upper right control points are derived(or obtained) based on the first index value (S4905). In one embodiment,the MVD horizontal component of the upper left control point may bederived by performing a right shift operation by 2 for the first index,and the MVD horizontal component of the upper right control point may bederived by performing an AND operation of the first index and 2.

If the first index value is (0, 0), the decoder increases the layer to anext layer (i.e., the third layer) and then parses layer and/or indexinformation (S4906). In an embodiment, the layer and index informationmay be parsed using an exponential Golomb code having an exponentialGolomb parameter of 1 (i.e., order of 1). Then, the decoder identifieswhether it is included in the third layer based on the index information(S4907 and S4909) and determines an exact combination of MVDx based onthe index information in the layer determined based thereupon (S4908,S4910, and S4911). The index information in step S4906 may be a firstindex or a second index that is additionally parsed in step S4906.

The decoder parses sign information for the final MVDx values of theupper left and upper right control points (S4912). When theabove-described process is complete, the decoder derives the MVDvertical component by performing the step of determiningMVDy_LT_MVDy_RT_Vector_Level (i.e., S4802 in FIG. 48).

To integrate a more general structure, a coding structure resultant frommodifying the conventional structure by the above-described embodimentsis described below.

FIG. 50 is a view illustrating a coding structure of a motion vectordifference performed based on vector coding according to an embodimentof the disclosure.

Referring to FIG. 50, the following description focuses primarily on adecoder for convenience of description, but the disclosure is notlimited thereto, and the method of signaling affine motion vectordifference information according to an embodiment of the disclosure maybe performed in an encoder and a decoder in substantially the samemanner. No duplicate description related to FIG. 55 is given below.

In the embodiment of the disclosure, the decoder parses the Layerx_GT0flag indicating whether it is larger than a first layer (the layerhaving a layer value of 0) (S5001) and, if the Layerx_GT0 flag is true(S5002), parses the Layerx_GT1 layer indicating whether it is largerthan a second layer (the layer having a layer value of 1) (S5503).

If the value of Layerx_GT1 is 0 (i.e., when belonging to the firstlayer), the decoder parses a first index and decodes the horizontalcomponent of the MVD based on the value of the index (S5004 to S5008).In this case, the value of the first index may have a value of 0 or 1.If it has a value of 0, the horizontal components of the MVDs of theupper left and upper right control points all may have a value of 1.Otherwise, it may be determined as a combination of (1, 0) or (0, 1).

If the value of Layerx_GT1 is 1, the decoder parses the remaining layerinformation indicating a specific layer among the subsequent layers anda second index (S5009). The remaining layer may have a value obtained bysubtracting 2 from the current layer (or the final layer). In oneembodiment, the decoder may decode the remaining layer informationand/or the second index using an exponential Golomb code having anexponential Golomb parameter of 1 (i.e., order of 1) and/or truncatedbinarization (TB) (or truncated unary binarization). Further, thedecoder may determine the current layer by adding the remaining layer tothe first layer value.

The decoder identifies whether the second index is less than or equal tothe current layer (S5010). Once the index is decoded, a combination ofMVD values needs to be determined. To this end, an additional check maybe performed to determine an exact MVD combination, i.e., whether theindex is equal to or smaller than the layer ID. According to the resultof the check, the MVD (LTx, RTx) having the second index smaller than orequal to the current layer may be determined to have a value equal to(index, Layer Id) (S5011).

The decoder identifies whether the second index is less than twice thecurrent layer (S5012). If the index is less than twice the layer, MVD(LTx, RTx) may be determined to have the same value as (Layer Id,2*Layer Id−index) (S5013). Otherwise, the MVD (LTx, RTx) may bedetermined to have the same value as (Layer Id+2*Layer Id−index, 2*LayerId−index) (S5014). Then, sign information is parsed (S5015). The layerinformation and index coding described above are examples, and thedisclosure is not limited thereto.

As an embodiment of the disclosure, the following methods may be appliedto the embodiments described above.

-   -   Context model may be varied    -   Different binarization techniques may be applied.    -   When exponential Golomb code is used, different Golomb orders        may be used.    -   Layer information and index may be coded with only the        exponential Golomb code.

Embodiment 5

In an embodiment of the disclosure, a method for jointly coding MVDs forx and y components using vector coding techniques is proposed. In theabove-described embodiment, the correlation between the horizontal andvertical components of the MVDs of the left (LT) and right (RT) controlpoints is used only for the affine motion model. Hereinafter, ageneralized MVD coding method that is not limited to the affine motionmodel and retains the previously described layer and index concept isproposed.

FIG. 51 is a view illustrating a vector coding method for a motionvector difference according to an embodiment of the disclosure.

FIG. 51 may be derived using data statistics using frequency analysis.Referring to FIG. 51, it is shown that when the x-MVD components (i.e.,the horizontal direction components of the MVD) are divided for they-MVD components, each layer may form a rhombus shape. In the structureillustrated in FIG. 51, the center point (i.e., the position where thevalue is 0) indicates the position where the MVDx and MVDy values are 0(i.e., 0,0 marked next to FIG.).

The center point (0,0) corresponds to an MVD combination that mostfrequently occurs in the data set. In this case, FIG. 51 may be regardedas a grid having positive and negative MVD values, and in a blockadjacent to the center point, the MVD value may increase or decreasealong the horizontal or vertical axis.

According to the data frequency analysis, the MVD values of a specificgroup may occur with similar probabilities. As a result, according to anembodiment of the disclosure, a layer representing MVD combinationshaving similar probabilities may be defined. The layers illustrated inFIG. 51 are an example, and may be extended to include several otherlayers. Further, in this embodiment, sign information may not beseparately coded, which may save signaling bits. As an embodiment, theMVD may be encoded/decoded using layer and index information.

FIG. 52 is a view illustrating a vector coding method for a motionvector difference based on a layer structure according to an embodimentof the disclosure.

Referring to FIG. 52, for convenience of description in applying anembodiment of the disclosure, the description focuses primarily on adecoder, but the MVD coding method according to an embodiment of thedisclosure may be applied to an encoder in substantially the samemanner.

Referring to FIG. 52, to decode the MVD of the current block, thedecoder first parses a Layer GRT0 flag indicating whether the layer isgreater than 0 (S5201). In the disclosure, the layer (or layer ID) mayhave an integer (i.e., 0, 1, 2, 3, 4, . . . ) in ascending order from 0.In the disclosure, when the layer is 0, the layer is a layer that comesfirst and may be referred to as the first layer, and similarly, when thelayer is 1, the layer is a layer that comes second and may be referredto as the second layer. That is, a layer ID and a layer order may have adifference of 1 in value. When the Layer GRT0 flag is 0 (i.e., false),both the MVDx and MVDy values may be determined to be 0.

If the Layer GRT0 flag is true, the decoder parses the Layer GRT1 flag(S5202 and S5203). In the disclosure, the Layer GRT0 flag and the LayerGRT1 flag are not limited by their names. If the Layer GRT1 flag istrue, the current layer is 2 or more, and the decoder parses Rem_Layerindicating the remaining layer information (S5205). The remaining layer(i.e., Rem_Layer) may be a value obtained by subtracting 2 from thecurrent layer (or the final layer). In one embodiment, the decoder maydecode the remaining layer information using an exponential Golomb codehaving an exponential Golomb parameter of 1 (i.e., order of 1) and/ortruncated binarization (TB) (or truncated unary binarization). When theLayer GRT1 flag is true, the current layer is 1, and the index to bedecoded may be placed in the second layer.

The decoder parses an index indicating a specific MVD combination in thedetermined current layer (S5206). In one embodiment, the decoder maydecode the index using an exponential Golomb code having an exponentialGolomb parameter of 1 (i.e., order of 1) and/or truncated binarization(TB) (or truncated unary binarization).

The decoder derives the MVD based on the determined current layer andindex values (S5207).

According to conventional video compression techniques, the horizontalcomponent (x) and the vertical component (y) of the MVD are individuallyencoded/decoded. However, as described above, according to data analysisbased on frequency analysis, the horizontal component and the verticalcomponent of the MVD may have a mutual correlation and are highly likelyto belong to the same layer in the layer structure according to anembodiment of the disclosure.

Accordingly, according to an embodiment of the disclosure, the MVDcoding efficiency may be significantly increased by coding thehorizontal and vertical components of the MVD together based on layerinformation and index information.

Embodiment 6

In one embodiment of the disclosure, a specific method for finallyderiving MVD based on the index parsed in the decoding structure ofembodiment 5 is described. That is, in steps S5206 and S5207 of FIG. 52described above, the MVD (x, y) value may be determined according to amethod as described below. In the disclosure, for convenience ofdescription, layer may be referred to as Lyr, and index may be referredto as idx.

First, when the layer is 1, MVDs in the horizontal and verticaldirections may be determined according to Equation 23 below.MVD _(x)=((idx≤Lyr)?idx:(Lyr<<1)−idx)MVD _(y)=((idx≤Lyr)?!idx:(idx==2?−1:0))  [Equation 23]

Referring to Equation 23, when idx≤Lyr, MVD_x may be determined as idx,and when idx>Lyr, MVD_x may be determined as (Lyr<<1)−idx. Here,<<denotes an operator of left shifting the left value by the rightvalue. When idx≤Lyr, MVDy may be determined as !idx, and when idx>Lyr,MVDy may be determined as (idx==2?−1:0).

First, when the layer is larger than 1, MVDs in the horizontal andvertical directions may be determined according to Equation 24 below.MVD _(x)=(idx≤Lyr?idx:(idx≤((Lyr<<1)+Lyr)?(Lyr<<1)−idx:idx−(Lyr<<2))MVD _(y)=((idx≤(Lyr<<1))?Lyr−idx:idx−((Lyr<<1)+Lyr))  [Equation 24]

Referring to Equation 24, when idx≤Lyr, MVD_x may be determined as idx,and when idx>Lyr, MVD_x is (idx≤((Lyr<<1)Lyr)?(Lyr<<1)−idx:idx−(Lyr<<2). When idx≤(Lyr<<1), MVD_y may bedetermined as Lyr-idx, and when idx>(Lyr<<1), MVD_y may be determined asidx−((Lyr<<1) Lyr).

Likewise, the index within the layer may be determined according to amethod as described below. As an embodiment, it may be determined by theencoder according to the following method, or it may be predefined inthe encoder and the decoder in the same method.

First, when MVD_x and MVD_y are 0, the layer (or layer ID) may bedetermined as 0.

If the layer is 1, the index may be determined (or calculated) usingEquation 25 below.idx=(MVD _(x)≥0)?(Lyr−MVD _(y)):(Lyr<<1)−MVD _(x))  [Equation 25]

Referring to Equation 25, when MVD_x is greater than or equal to 0, theindex may be derived as Lyr−MVD_y, otherwise, the index may be derivedas (Lyr<<1)−MVD_x.

If the layer is greater than 1, the index may be derived using Equation26 below.idx=(MVD _(x)≥0)?(Lyr−MVD _(y)):((MVD _(y)≤0)?((Lyr<<1)−MVD_(x)):(((Lyr<<1)+Lyr)+MVD _(y)))  [Equation 26]

Referring to Equation 26, when MVD_x is greater than or equal to 0, theindex may be derived as Lyr−MVD_y, otherwise, the index may be derivedas (MVD_y≤0)?((Lyr<<1)−MVD_x):((((Lyr<<1) Lyr)+MVD_y).

In one embodiment, Table 4 below illustrates a layer and index tableaccording to a combination of horizontal and vertical components of theMVD. That is, the index value may be allocated according to acombination of the horizontal and vertical components of the MVD asshown in Table 4 below by applying the above-described methods.

TABLE 4 MVD_(x) MVD_(y) Layer Index 0 0 0 — 0 1 1 0 1 0 1 1 0 −1 1 2 −10 1 3 0 2 2 0 1 1 2 1 2 0 2 2 1 −1 2 3 0 −2 2 4 −1 −1 2 5 −2 0 2 6 −1 12 7 . . . . . . . . . . . .

FIG. 53 is a view illustrating an example structure of a decodingapparatus according to an embodiment of the disclosure.

The decoding apparatus illustrated in FIG. 53 may be included in theencoding apparatus 200 of FIG. 2 (or the inter predictor 260 or themotion information derivation unit 262 of FIG. 11).

The layer and index information receiver (or a receiving component) 121may receive layer and index information. In this case, the methodsdescribed above in connection with Embodiments 5 and 6 may be applied.

The MVDx and MVDy processor (or a processing component) 122 may decodeMVDx and MVDy using the determined layer information and indexinformation. As an example, Equations 23 to 26 described above may beused to determine the MVDx and MVDy components.

FIG. 54 is a view illustrating an example structure of an encodingapparatus according to an embodiment.

The encoding apparatus illustrated in FIG. 54 may be included in theencoding apparatus 100 of FIG. 1 (or the inter predictor 180 or themotion information derivation unit 182 of FIG. 9).

The encoding apparatus may perform operations opposite to theabove-described operations of the decoding apparatus.

First, the input receiver 131 receives a signed MVD (x, y) as an inputfor entropy coding.

The layer and index information generator (or a generating component)132 generates layer and index information. As an example, Equations 23to 26 described above may be used to determine layer and indexinformation.

Thereafter, the entropy encoder (or a component for entropy coding) 133entropy-codes the determined layer and index information.

The embodiments of the disclosure described above have been separatelydescribed for convenience of description, but the disclosure is notlimited thereto. In other words, the embodiments described above inconnection with embodiments 1 to 5 may be performed independently or incombination of one or more thereof.

FIG. 55 is a flowchart illustrating a method for processing a videosignal based on inter prediction according to an embodiment of thedisclosure.

Referring to FIG. 55, the following description focuses primarily on adecoder for convenience of description, but the disclosure is notlimited thereto. The method for processing video signals based on interprediction according to embodiments of the disclosure may be performedin an encoder and a decoder in the same manner.

The decoder derives a motion vector predictor using motion informationfor a neighboring block of a current block (S5501).

The decoder parses layer information indicating a current layer to whicha motion vector difference used for inter prediction of the currentblock belongs, in a predefined layer structure (S5502). Here, in thelayer structure, a combination of at least one horizontal and verticaldirections (or components) of motion vector differences may be dividedinto a plurality of layers.

The decoder parses index information indicating a specific combinationin the current layer (S5503).

The decoder derives a motion vector difference of the current blockusing the layer information and the index information (S5504).

The decoder derives a motion vector of the current block by adding themotion vector difference to the motion vector predictor (S5505).

As described above, parsing the layer information may include parsing afirst flag indicating whether an identification (ID) of the currentlayer is larger than 0 and, when the ID of the current layer is 0,parsing a second flag indicating whether the ID of the current layer islarger than 1.

As described above, parsing the layer information may include parsingremaining layer information indicating the current layer among layerswhose IDs are equal to or larger than 2 when the ID of the current layeris larger than 1.

As described above, the remaining layer information may be binarizedusing an exponential Golomb code having an order of 1.

As described above, the index information may be binarized using atruncated binarization method.

As described above, the method may further comprise generating aprediction sample of the current block by performing inter predictionusing the motion vector of the current block.

FIG. 56 is a block diagram illustrating an example device for processingvideo signals according to an embodiment of the disclosure. The imagesignal processing device of FIG. 56 may correspond to the encodingdevice 100 of FIG. 1 or the decoding device 200 of FIG. 2.

The video signal processing device 5600 for processing video signals mayinclude a memory 5620 for storing video signals and a processor 5610coupled with the memory to process video signals.

According to an embodiment of the disclosure, the processor 5610 may beconfigured as at least one processing circuit for processing imagesignals and may execute instructions for encoding or decoding imagesignals to thereby process image signals. In other words, the processor5610 may encode raw image data or decode encoded image signals byexecuting encoding or decoding methods described above.

FIG. 57 illustrates a video coding system to which the disclosure isapplied.

A video coding system may include a source device and a receivingdevice. The source device may forward encoded video/image information ordata to the receiving device in a file or streaming format through adigital storage medium or a network.

The source device may include a video source, an encoding apparatus anda transmitter. The receiving device may include a receiver, a decodingapparatus and a renderer. The encoding apparatus may be called avideo/image encoding apparatus, and the decoding apparatus may be calleda video/image decoding apparatus. The transmitter may be included in theencoding apparatus. The receiver may be included in the decodingapparatus. The renderer may include a display unit, and the display unitmay be constructed as an independent device or an external component.

The video source may obtain video/image through processes such ascapturing, composing or generating. The video source may include avideo/image capturing device and/or a video/image generating device. Thevideo/image capturing device may include one or more cameras,video/image archive including a video/image captured previously, and thelike, for example. The video/image generating device may include acomputer, a tablet and a smart phone, for example, and may generatevideo/image (electrically), for example. For example, a virtualvideo/image may be generated through a computer, and in this case, thevideo/image capturing process may be substituted by the process ofgenerating a related data.

The encoding apparatus may encode an input video/image. The encodingapparatus may perform a series of processes including a prediction, atransform, a quantization, and the like for compression and codingefficiency.

The transmitter may forward encoded video/image information or dataoutput in a bitstream format to the receiver of the receiving device ina file or streaming format through a digital storage medium or anetwork. The digital storage medium may include various storage mediasuch as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like. Thetransmitter may include an element for generating a media file through apredetermined file format and may include an element for transmittingthrough broadcasting/communication network. The receiver may extract thebitstream and forward it to the decoding apparatus.

The decoding apparatus may perform a series of processes including adequantization, an inverse transform, a prediction, and the like thatcorresponds to the operation of the encoding apparatus and decodevideo/image.

The renderer may render the decoded video/image. The renderedvideo/image may be displayed through the display unit.

FIG. 58 is a configuration diagram of a content streaming system as anembodiment to which the disclosure is applied.

Referring to FIG. 58, the content streaming system to which thedisclosure is applied may include an encoding server, a streamingserver, a web server, a media storage, a user equipment, and multimediainput devices.

The encoding server serves to compress content input from multimediainput devices such as a smartphone, a camera and a camcorder intodigital data to generate a bitstream and transmit the bitstream to thestreaming server. As another example, when the multimedia input devicessuch as a smartphone, a camera and a camcorder directly generatebitstreams, the encoding server may be omitted.

The bitstream may be generated by an encoding method or a bitstreamgeneration method to which the disclosure is applied and the streamingserver can temporarily store the bitstream in the process oftransmitting or receiving the bitstream.

The streaming server transmits multimedia data to the user equipment onthe basis of a user request through the web server and the web serverserves as a medium that informs a user of services. When the user sendsa request for a desired service to the web server, the web serverdelivers the request to the streaming server and the streaming servertransmits multimedia data to the user. Here, the content streamingsystem may include an additional control server, and in this case, thecontrol server serves to control commands/responses between devices inthe content streaming system.

The streaming server may receive content from the media storage and/orthe encoding server. For example, when content is received from theencoding server, the streaming server can receive the content in realtime. In this case, the streaming server may store bitstreams for apredetermined time in order to provide a smooth streaming service.

Examples of the user equipment may include a cellular phone, asmartphone, a laptop computer, a digital broadcast terminal, a PDA(personal digital assistant), a PMP (portable multimedia player), anavigation device, a slate PC, a tablet PC, an Ultrabook, a wearabledevice (e.g., a smartwatch, a smart glass and an HMD (head mounteddisplay)), a digital TV, a desktop computer, a digital signage, etc.

Each server in the content streaming system may be operated as adistributed server, and in this case, data received by each server canbe processed in a distributed manner.

The embodiments described in the disclosure may be implemented andperformed on a processor, a microprocessor, a controller or a chip. Forexample, the function units illustrated in the drawings may beimplemented and performed on a computer, a processor, a microprocessor,a controller or a chip.

Furthermore, the decoder and the encoder to which the disclosure isapplied may be included in a multimedia broadcasting transmission andreception device, a mobile communication terminal, a home cinema videodevice, a digital cinema video device, a camera for monitoring, a videodialogue device, a real-time communication device such as videocommunication, a mobile streaming device, a storage medium, a camcorder,a video on-demand (VoD) service provision device, an over the top (OTT)video device, an Internet streaming service provision device, athree-dimensional (3D) video device, a video telephony device, and amedical video device, and may be used to process a video signal or adata signal. For example, the OTT video device may include a gameconsole, a Blu-ray player, Internet access TV, a home theater system, asmartphone, a tablet PC, and a digital video recorder (DVR).

Furthermore, the processing method to which the disclosure is appliedmay be produced in the form of a program executed by a computer, and maybe stored in a computer-readable recording medium. Multimedia datahaving a data structure according to the disclosure may also be storedin a computer-readable recording medium. The computer-readable recordingmedium includes all types of storage devices in which computer-readabledata is stored. The computer-readable recording medium may includeBlu-ray disk (BD), a universal serial bus (USB), a ROM, a PROM, anEPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, andan optical data storage device, for example. Furthermore, thecomputer-readable recording medium includes media implemented in theform of carriers (e.g., transmission through the Internet). Furthermore,a bit stream generated using an encoding method may be stored in acomputer-readable recording medium or may be transmitted over wired andwireless communication networks.

Furthermore, an embodiment of the disclosure may be implemented as acomputer program product using program code. The program code may beperformed by a computer according to an embodiment of the disclosure.The program code may be stored on a carrier readable by a computer.

In the aforementioned embodiments, the elements and characteristics ofthe disclosure have been combined in a specific form. Each of theelements or characteristics may be considered to be optional unlessotherwise described explicitly. Each of the elements or characteristicsmay be implemented in a form to be not combined with other elements orcharacteristics. Furthermore, some of the elements and/or thecharacteristics may be combined to form an embodiment of the disclosure.The sequence of the operations described in the embodiments of thedisclosure may be changed. Some of the elements or characteristics of anembodiment may be included in another embodiment or may be replaced withcorresponding elements or characteristics of another embodiment. It isevident that an embodiment may be constructed by combining claims nothaving an explicit citation relation in the claims or may be included asa new claim by amendments after filing an application.

The embodiment according to the disclosure may be implemented by variousmeans, for example, hardware, firmware, software or a combination ofthem. In the case of an implementation by hardware, the embodiment ofthe disclosure may be implemented using one or more application-specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, etc.

In the case of an implementation by firmware or software, the embodimentof the disclosure may be implemented in the form of a module, procedureor function for performing the aforementioned functions or operations.Software code may be stored in the memory and driven by the processor.The memory may be located inside or outside the processor and mayexchange data with the processor through a variety of known means.

It is evident to those skilled in the art that the disclosure may bematerialized in other specific forms without departing from theessential characteristics of the disclosure. Accordingly, the detaileddescription should not be construed as being limitative, but should beconstrued as being illustrative from all aspects. The scope of thedisclosure should be determined by reasonable analysis of the attachedclaims, and all changes within the equivalent range of the disclosureare included in the scope of the disclosure.

INDUSTRIAL APPLICABILITY

The aforementioned preferred embodiments of the disclosure have beendisclosed for illustrative purposes, and those skilled in the art mayimprove, change, substitute, or add various other embodiments withoutdeparting from the technical spirit and scope of the disclosuredisclosed in the attached claims.

The invention claimed is:
 1. A method for processing a video signalbased on inter prediction by an apparatus, the method comprising:deriving a motion vector predictor based on motion information for aneighboring block of a current block; parsing layer informationindicating a current layer to which a motion vector difference used forinter prediction of the current block belongs, in a predefined layerstructure in which combinations of at least one horizontal and verticalcomponents of motion vector differences are divided into a plurality oflayers; parsing index information indicating a specific combination inthe current layer; deriving a motion vector difference of the currentblock using the layer information and the index information; andderiving a motion vector of the current block by adding the motionvector difference to the motion vector predictor, wherein parsing thelayer information includes: parsing a first flag indicating whether anidentification (ID) of the current layer is larger than 0, and parsing asecond flag indicating whether the ID of the current layer is largerthan 1 when the ID of the current layer is larger than
 0. 2. The methodof claim 1, wherein parsing the layer information includes parsingremaining layer information indicating the current layer among layerswhose IDs are equal to or larger than 2 when the ID of the current layeris larger than
 1. 3. The method of claim 2, wherein the remaining layerinformation is binarized using an exponential Golomb code having anorder of
 1. 4. The method of claim 1, wherein the index information isbinarized using a truncated binarization scheme.
 5. The method of claim1, further comprising: generating a prediction sample of the currentblock by performing inter prediction using the motion vector of thecurrent block.
 6. A method of encoding a video signal based on interprediction by an apparatus, the method comprising: deriving a motionvector of a current block based on the inter prediction; deriving amotion vector predictor based on motion information for a neighboringblock of the current block; generating a motion vector difference of thecurrent block based on the motion vector and the motion vector predictorof the current block; generating layer information indicating a currentlayer to which the motion vector difference belongs, in a predefinedlayer structure in which combinations of at least one horizontal andvertical components of motion vector differences are divided into aplurality of layers; and generating index information indicating aspecific combination in the current layer, wherein generating the layerinformation includes: generating a first flag indicating whether anidentification (ID) of the current layer is larger than 0, andgenerating a second flag indicating whether the ID of the current layeris larger than 1 when the ID of the current layer is larger than
 0. 7.The method of claim 6, wherein generating the layer informationincludes: generating remaining layer information indicating the currentlayer among layers whose IDs are equal to or larger than 2 when the IDof the current layer is larger than
 1. 8. The method of claim 7, furthercomprising: binarizing the remaining layer information using anexponential Golomb code having an order of
 1. 9. The method of claim 6,further comprising: binarizing the index information using a truncatedbinarization scheme.
 10. The method of claim 6, further comprising:generating a residual sample of the current block by performing theinter prediction using the motion vector of the current block.
 11. Anon-transitory computer-readable storage medium for encoded imageinformation generated by performing steps of: deriving a motion vectorof a current block based on inter prediction; deriving a motion vectorpredictor based on motion information for a neighboring block of thecurrent block; generating a motion vector difference of the currentblock based on the motion vector and the motion vector predictor of thecurrent block; generating layer information indicating a current layerto which the motion vector difference belongs, in a predefined layerstructure in which combinations of at least one horizontal and verticalcomponents of motion vector differences are divided into a plurality oflayers; and generating index information indicating a specificcombination in the current layer, wherein generating the layerinformation includes: generating a first flag indicating whether anidentification (ID) of the current layer is larger than 0, andgenerating a second flag indicating whether the ID of the current layeris larger than 1 when the ID of the current layer is larger than 0.